Zoom lens and optical apparatus having the same

ABSTRACT

A zoom lens is constructed with, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit including a negative meniscus lens having a concave surface facing the image side and a positive meniscus lens having a convex surface facing the object side, a second lens unit of positive optical power, the second lens unit including a cemented lens of positive optical power as a whole disposed on the most image side of the second lens unit, and a lens having a concave surface facing the image side and adjoining a surface on the object side of the cemented lens, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a zoom lens and an opticalapparatus having the zoom lens, and more particularly to a zoom lenssuited for a film still camera, a video camera, a digital still cameraor the like, which has three lens units in which a lens unit of negativerefractive power leads, and which has the entirety of a lens systemthereof reduced in size by appropriately setting the lens constructionof the respective lens units.

[0003] 2. Description of Related Art

[0004] In recent years, with the advancement of high performance of animage pickup apparatus (camera), such as a video camera or a digitalstill camera, using a solid-state image sensor, a zoom lens having alarge aperture ratio including a wide angle of view is desired for thepurpose of being used for an optical system of such an image pickupapparatus. Since, in such an image pickup apparatus, a variety ofoptical members, including a low-pass filter, a color correction filter,etc., are disposed between the rearmost portion of the zoom lens and theimage sensor, a lens system having a relatively long back focal distanceis required for the optical system. In addition, in the case of a colorcamera using an image sensor for color images, a zoom lens excellent intelecentricity on the image side is desired for an optical system of thecolor camera so as to prevent color shading.

[0005] Heretofore, there have been proposed a variety of wide-angletwo-unit zoom lenses of the so-called short zoom type each of which iscomposed of a first lens unit of negative refractive power and a secondlens unit of positive refractive power, the separation between the firstlens unit and the second lens unit being varied to effect the variationof magnification. In such an optical system of the short zoom type, thevariation of magnification is effected by moving the second lens unit ofpositive refractive power, and the compensation for the shift of animage point due to the variation of magnification is effected by movingthe first lens unit of negative refractive power.

[0006] In such a lens construction composed of two lens units, the zoommagnification thereof is 2× or thereabout. Further, in order to make theentirety of a lens system in a compact form while having a high variablemagnification ratio greater than 2×, there have been proposed, forexample, in Japanese Patent Publication No. Hei 7-3507 (corresponding toU.S. Pat. No. 4,810,072), Japanese Patent Publication No. Hei 6-40170(corresponding to U.S. Pat. No. 4,647,160), etc., the so-calledthree-unit zoom lenses in each of which a third lens unit of negative orpositive refractive power is disposed on the image side of the two-unitzoom lens so as to correct the various aberrations occurring due to thehigh variable magnification.

[0007] Further, in U.S. Pat. No. 4,828,372 and No. 5,262,897, there isdisclosed a three-unit zoom lens in which the second lens unit iscomposed of six lens elements, as a whole, including two cementedlenses, thereby attaining the high variable magnification of 3× or more.

[0008] Three-unit zoom lenses satisfying both the back focal distanceand the telecentric characteristic have been proposed in, for example,Japanese Laid-Open Patent Application No. Sho 63-135913 (correspondingto U.S. Pat. No. 4,838,666), Japanese Laid-Open Patent Application No.Hei 7-261083, etc. In addition, in Japanese Laid-Open Patent ApplicationNo. Hei 3-288113 (corresponding to U.S. Pat. No. 5,270,863), there isdisclosed a three-unit zoom lens in which a first lens unit of negativerefractive power is fixed and a second lens unit of positive refractivepower and a third lens unit of positive refractive power are moved toeffect the variation of magnification. However, in these zoom lenses,there are such drawbacks that the number of constituent lens elements ofeach lens unit is relatively large, the total length of the lens systemis great, and the production cost is high.

[0009] Further, in recent years, there has been widely used theso-called barrel-retractable zoom lens in which, in order to make thecompactness of a camera and the high magnification of a lens systemcompatible with each other, the separation between the respectiveadjacent lens units at the time of nonuse of the camera is reduced up tothe separation different from that at the time of use of the camera,thereby lessening the amount of protrusion of the zoom lens from thecamera body. However, in a case where, as in the conventional zoomlenses, the number of constituent lens elements of each lens unit islarge and, as a result, the length of each lens unit on the optical axisis great, or in a case where the amount of movement of each lens unitduring zooming and during focusing is large and the total lens lengthis, therefore, great, it is sometimes impossible to attain the desiredlength of the zoom lens as retracted.

[0010] Further, in the zoom lens disclosed in Japanese Laid-Open PatentApplication No. Hei 7-261083, a convex lens (positive lens) is disposedon the most object side of the first lens unit of negative refractivepower, so that there is such a drawback that an increase of the outerdiameter of the zoom lens when made to have a wide angle is inevitable.In addition, in this zoom lens, since the focusing onto a close objectis effected by moving the first lens unit of negative refractive power,there is such a drawback that the construction of a lens mountingmechanism is complicated in combination with the movement for zooming.

[0011] Further, in U.S. Pat. No. 4,999,007, there is disclosed athree-unit zoom lens in which each of the first lens unit and the secondlens unit is composed of a single lens. However, in this zoom lens, thetotal lens length at the wide-angle end is relatively great, and,because the distance between the first lens unit and the stop at thewide-angle end is large, the height of incidence of an off-axial ray oflight is large to increase the diameter of a lens element of the firstlens unit. Therefore, there is such a drawback that the entirety of alens system becomes large.

BRIEF SUMMARY OF THE INVENTION

[0012] In view of the above-mentioned drawbacks of the conventional zoomlenses, an object of the invention is to provide a zoom lens which issuited for a photographic system using a solid-state image sensor, has ahigh variable magnification ratio despite being compact and small indiameter with less constituent lens elements, and has excellent opticalperformance, and to provide an optical apparatus having the zoom lens.

[0013] To attain the above object, in accordance with an aspect of theinvention, there is provided a zoom lens, which comprises, in order froman object side to an image side, a first lens unit of negative opticalpower, the first lens unit including a negative meniscus lens having aconcave surface facing the image side and a positive meniscus lenshaving a convex surface facing the object side, a second lens unit ofpositive optical power, the second lens unit including a cemented lensof positive optical power as a whole disposed on the most image side ofthe second lens unit, and a lens having a concave surface facing theimage side and adjoining a surface on the object side of the cementedlens, and a third lens unit of positive optical power, wherein aseparation between the first lens unit and the second lens unit and aseparation between the second lens unit and the third lens unit arevaried to effect variation of magnification.

[0014] In accordance with another aspect of the invention, there isprovided a zoom lens, which comprises, in order from an object side toan image side, a first lens unit of negative optical power, the firstlens unit including a negative meniscus lens having a concave surfacefacing the image side and a positive meniscus lens having a convexsurface facing the object side, a second lens unit of positive opticalpower, the second lens unit including a negative lens of bi-concaveform, a positive lens disposed on the object side of the negative lensof bi-concave form and having a convex surface facing the object side,and a cemented lens of positive optical power as a whole disposed on theimage side of the negative lens of bi-concave form, and a third lensunit of positive optical power, wherein a separation between the firstlens unit and the second lens unit and a separation between the secondlens unit and the third lens unit are varied to effect variation ofmagnification.

[0015] In accordance with a further aspect of the invention, there isprovided a zoom lens, which comprises, in order from an object side toan image side, a first lens unit of negative optical power, the firstlens unit including a negative meniscus lens having a concave surfacefacing the image side and a positive meniscus lens having a convexsurface facing the object side, a second lens unit of positive opticalpower, the second lens unit including, in order from the object side tothe image side, one or two positive lenses, a negative lens ofbi-concave form, and a cemented lens of positive optical power as awhole, and a third lens unit of positive optical power, wherein aseparation between the first lens unit and the second lens unit and aseparation between the second lens unit and the third lens unit arevaried to effect variation of magnification, and wherein the zoom lenssatisfies the following conditions:

0.5<fc/f2<2.0

0.5<(Ra+Rb)/(Ra+Rb)<2.5

0.3<|fn|/f2<2.0

0.5<(Rd+Rc)/(Rd−Rc)<2.5

[0016] where fc is a focal length of the cemented lens in the secondlens unit, fn is a focal length of the negative lens in the second lensunit, f2 is a focal length of the second lens unit, Ra is a radius ofcurvature of a surface on the object side of the cemented lens in thesecond lens unit, Rb is a radius of curvature of a surface on the imageside of the negative lens in the second lens unit, and Rc and Rd areradii of curvature of lens surfaces on the object side and the imageside, respectively, of the positive lens disposed on the most objectside of the second lens unit.

[0017] In accordance with a still further aspect of the invention, thereis provided a zoom lens, which comprises, in order from an object sideto an image side, a first lens unit of negative optical power, the firstlens unit including a negative lens and a positive lens, a second lensunit of positive optical power, the second lens unit consisting of acemented lens and one positive lens, and a third lens unit of positiveoptical power, the third lens unit including a positive lens, wherein aseparation between the first lens unit and the second lens unit and aseparation between the second lens unit and the third lens unit arevaried to effect variation of magnification.

[0018] In accordance with a still further aspect of the invention, thereis provided a zoom lens, which comprises, in order from an object sideto an image side, a first lens unit of negative optical power, a secondlens unit of positive optical power, and a third lens unit of positiveoptical power, the third lens unit consisting of one or two lensesincluding a positive lens, wherein a separation between the first lensunit and the second lens unit and a separation between the second lensunit and the third lens unit are varied to effect variation ofmagnification, and wherein the zoom lens satisfies the followingconditions:

ndp3<1.5

νdp3>70.0

[0019] where ndp3 and νdp3 are a refractive index and Abbe number,respectively, of material of the positive lens in the third lens unit.

[0020] In accordance with a still further aspect of the invention, thereis provided a zoom lens, which comprises, in order from an object sideto an image side, a first lens unit of negative optical power, a secondlens unit of positive optical power, and a third lens unit of positiveoptical power; wherein a separation between the first lens unit and thesecond lens unit and a separation between the second lens unit and thethird lens unit are varied to effect variation of magnification, andwherein, during the variation of magnification from a wide-angle end toa telephoto end with an infinitely distant object focused on, the thirdlens unit moves monotonically toward the image side or moves with alocus convex toward the image side, and the zoom lens satisfies thefollowing condition:

0.08<M3/fw<0.4

[0021] where M3 is an amount of movement of the third lens unit towardthe image side during the variation of magnification from the wide-angleend to the telephoto end with an infinitely distant object focused on,and fw is a focal length of the zoom lens at the wide-angle end.

[0022] In accordance with a still further aspect of the invention, thereis provided a zoom lens, which comprises, in order from an object sideto an image side, a first lens unit of negative optical power, the firstlens unit consisting of, in order from the object side to the imageside, a negative lens and a positive lens, a second lens unit ofpositive optical power, and a third lens unit of positive optical power,wherein a separation between the first lens unit and the second lensunit and a separation between the second lens unit and the third lensunit are varied to effect variation of magnification, wherein, with aninfinitely distant object focused on, the third lens unit is locatednearer to the image side at a telephoto end than at a wide-angle end,and wherein the zoom lens satisfies the following condition:

0.7<|f1/ft|<1.0

[0023] where f1 is a focal length of the first lens unit, and ft is afocal length of the zoom lens at the telephoto end.

[0024] In accordance with a still further aspect of the invention, thereis provided a zoom lens, which comprises, in order from an object sideto an image side, a first lens unit of negative optical power, the firstlens unit consisting of, in order from the object side to the imageside, a negative lens and a positive lens, a second lens unit ofpositive optical power, and a third lens unit of positive optical power,focusing being effected by moving the third lens unit, wherein aseparation between the first lens unit and the second lens unit and aseparation between the second lens unit and the third lens unit arevaried to effect variation of magnification, and wherein, during thevariation of magnification from a wide-angle end to a telephoto end withan infinitely distant object focused on, the third lens unit movesmonotonically toward the image side or moves with a locus convex towardthe image side, and the zoom lens satisfies the following conditions:

0.08<M3/fw<0.4

0.7<|f1/ft|<1.0

1.45<f3/ft<2.0

0.63<f2/ft<0.8

[0025] where M3 is an amount of movement of the third lens unit towardthe image side during the variation of magnification from the wide-angleend to the telephoto end with an infinitely distant object focused on,fw and ft are focal lengths of the zoom lens at the wide-angle end andthe telephoto end, respectively, and f1, f2 and f3 are focal lengths ofthe first lens unit, the second lens unit and the third lens unit,respectively.

[0026] Further, an optical apparatus according to the inventioncomprises a zoom lens set forth in accordance with any one of the aboveaspects of the invention.

[0027] The above and further objects and features of the invention willbecome apparent from the following detailed description of preferredembodiments thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0028]FIG. 1 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 1 of the invention.

[0029]FIGS. 2A to 2D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 1 ofthe invention.

[0030]FIGS. 3A to 3D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 1 of the invention.

[0031]FIGS. 4A to 4D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 1 ofthe invention.

[0032]FIG. 5 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 2 of the invention.

[0033]FIGS. 6A to 6D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 2 ofthe invention.

[0034]FIGS. 7A to 7D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 2 of the invention.

[0035]FIGS. 8A to 8D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 2 ofthe invention.

[0036]FIG. 9 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 3 of the invention.

[0037]FIGS. 10A to 10D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 3 ofthe invention.

[0038]FIGS. 11A to 11D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 3 of the invention.

[0039]FIGS. 12A to 12D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 3 ofthe invention.

[0040]FIG. 13 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 4 of the invention.

[0041]FIGS. 14A to 14D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 4 ofthe invention.

[0042]FIGS. 15A to 15D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 4 of the invention.

[0043]FIGS. 16A to 16D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 4 ofthe invention.

[0044]FIG. 17 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 5 of the invention.

[0045]FIGS. 18A to 18D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 5 ofthe invention.

[0046]FIGS. 19A to 19D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 5 of the invention.

[0047]FIGS. 20A to 20D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 5 ofthe invention.

[0048]FIG. 21 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 6 of the invention.

[0049]FIGS. 22A to 22D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 6 ofthe invention.

[0050]FIGS. 23A to 23D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 6 of the invention.

[0051]FIGS. 24A to 24D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 6 ofthe invention.

[0052]FIG. 25 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 7 of the invention.

[0053]FIGS. 26A to 26D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 7 ofthe invention.

[0054]FIGS. 27A to 27D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 7 of the invention.

[0055]FIGS. 28A to 28D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 7 ofthe invention.

[0056]FIG. 29 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 8 of the invention.

[0057]FIGS. 30A to 30D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 8 ofthe invention.

[0058]FIGS. 31A to 31D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 8 of the invention.

[0059]FIGS. 32A to 32D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 8 ofthe invention.

[0060]FIG. 33 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 9 of the invention.

[0061]FIGS. 34A to 34D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 9 ofthe invention.

[0062]FIGS. 35A to 35D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 9 of the invention.

[0063]FIGS. 36A to 36D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 9 ofthe invention.

[0064]FIG. 37 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 10 of the invention.

[0065]FIGS. 38A to 38D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 10 ofthe invention.

[0066]FIGS. 39A to 39D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 10 of the invention.

[0067]FIGS. 40A to 40D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 10 ofthe invention.

[0068]FIG. 41 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 11 of the invention.

[0069]FIGS. 42A to 42D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 11 ofthe invention.

[0070]FIGS. 43A to 43D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 11 of the invention.

[0071]FIGS. 44A to 44D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 11 ofthe invention.

[0072]FIG. 45 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 12 of the invention.

[0073]FIGS. 46A to 46D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 12 ofthe invention.

[0074]FIGS. 47A to 47D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 12 of the invention.

[0075]FIGS. 48A to 48D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 12 ofthe invention.

[0076]FIG. 49 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 13 of the invention.

[0077]FIGS. 50A to 50D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 13 ofthe invention.

[0078]FIGS. 51A to 51D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 13 of the invention.

[0079]FIGS. 52A to 52D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 13 ofthe invention.

[0080]FIG. 53 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 14 of the invention.

[0081]FIGS. 54A to 54D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 14 ofthe invention.

[0082]FIGS. 55A to 55D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 14 of the invention.

[0083]FIGS. 56A to 56D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 14 ofthe invention.

[0084]FIG. 57 is a lens block diagram showing a zoom lens at thewide-angle end according to a numerical example 15 of the invention.

[0085]FIGS. 58A to 58D are graphs showing aberration curves at thewide-angle end in the zoom lens according to the numerical example 15 ofthe invention.

[0086]FIGS. 59A to 59D are graphs showing aberration curves at themiddle focal length position in the zoom lens according to the numericalexample 15 of the invention.

[0087]FIGS. 60A to 60D are graphs showing aberration curves at thetelephoto end in the zoom lens according to the numerical example 15 ofthe invention.

[0088]FIG. 61 is a schematic diagram showing a video camera in which azoom lens according to the invention is used as a photographic opticalsystem.

DETAILED DESCRIPTION OF THE INVENTION

[0089] Hereinafter, preferred embodiments of the invention will bedescribed in detail with reference to the drawings.

[0090] According to the embodiments of the invention, there is provideda zoom lens which satisfies at least one of the following items.

[0091] (i) To correct well astigmatism and distortion at the wide-angleend, in particular.

[0092] (ii) To reduce the share of correcting aberration of a movinglens unit while taking the smallest lens construction, and to lessen thedeterioration of performance due to the decentering or the like of lensunits caused by manufacturing errors, thereby making it easy tomanufacture the zoom lens.

[0093] (iii) To attain a large aperture ratio suited for ahigh-density-pixel image sensor having low sensitivity.

[0094] (iv) To realize the good telecentric image formation on the imageside suited for a photographing system using a solid-state image sensorwhile minimizing the number of constituent lens elements of the zoomlens.

[0095] (v) To shorten the length on the optical axis of each lens unitrequired for the barrel-retractable zoom lens, and the amount ofmovement on the optical axis of each lens unit during zooming and duringfocusing.

[0096] (vi) To correct well distortion not only at the wide-angle endbut also over the entire range of zooming.

[0097] (vii) To lessen the variation of the image-side telecentric imageformation due to zooming.

[0098] (viii) To reduce the amount of movement of a variator lens unitwhile retaining the telecentric image formation, thereby attaining thefurther reduction in size.

[0099] (ix) To simplify a focusing mechanism for a close object.

[0100] (First Embodiment)

[0101]FIG. 1 to FIGS. 20A to 20D relate to a first embodiment of theinvention, which corresponds to numerical examples 1 to 5 of theinvention to be described later.

[0102]FIG. 1 is a lens block diagram showing a zoom lens according tothe numerical example 1 of the invention. FIGS. 2A to 2D through FIGS.4A to 4D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 1 of the invention.

[0103]FIG. 5 is a lens block diagram showing a zoom lens according tothe numerical example 2 of the invention. FIGS. 6A to 6D through FIGS.8A to 8D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 2 of the invention.

[0104]FIG. 9 is a lens block diagram showing a zoom lens according tothe numerical example 3 of the invention. FIGS. 10A to 10D through FIGS.12A to 12D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 3 of the invention.

[0105]FIG. 13 is a lens block diagram showing a zoom lens according tothe numerical example 4 of the invention. FIGS. 14A to 14D through FIGS.16A to 16D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 4 of the invention.

[0106]FIG. 17 is a lens block diagram showing a zoom lens according tothe numerical example 5 of the invention. FIGS. 18A to 18D through FIGS.20A to 20D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 5 of the invention.

[0107] In the lens block diagrams shown in FIGS. 1, 5, 9, 13 and 17,reference character L1 denotes a first lens unit of negative refractivepower, reference character L2 denotes a second lens unit of positiverefractive power, reference character L3 denotes a third lens unit ofpositive refractive power, reference character SP denotes an aperturestop for determining the brightness of an optical system, referencecharacter IP denotes an image plane, and reference character G denotes aglass block, such as a filter or a color separation prism.

[0108] In the basic construction of the zoom lens according to the firstembodiment, the first lens unit of negative refractive power and thesecond lens unit of positive refractive power constitute the so-calledshort zoom system, and the variation of magnification is effected bymoving the second lens unit of positive refractive power while the shiftof an image point due to the variation of magnification is compensatedfor by moving forward and backward the first lens unit of negativerefractive power. The third lens unit of positive refractive power, whenbeing made stationary during zooming (in the case of the numericalexample 5), does not contribute to the variation of magnification, butshares the increase of a refractive power of the photographic lens dueto the reduction in size of an image sensor so as to decrease arefractive power of the short zoom system composed of the first andsecond lens units. Therefore, in particular, it is possible to suppressthe occurrence of aberrations in lens elements constituting the firstlens unit, thereby attaining good optical performance. Further, theformation of a telecentric image on the image side required for an imagepickup apparatus using a solid-state image sensor or the like isattained by making the third lens unit of positive refractive power havethe role of a field lens. On the other hand, in a case where the thirdlens unit is made to move during zooming (in the cases of the numericalexamples 1 to 4), the height from the optical axis of an off-axial rayincident on the third lens unit can be controlled. Therefore, thefaculty of correcting the various off-axial aberrations is enhanced, sothat it is possible to realize good optical performance over the entirerange of variable magnification.

[0109] Further, the stop SP is disposed on the object side of the secondlens unit so as to shorten the distance between the entrance pupil andthe first lens unit at the wide-angle end, so that the outer diameter oflens elements constituting the first lens unit is prevented fromincreasing. In addition, the various off-axial aberrations are canceledby the first lens unit and the third lens unit between which the stop SPdisposed on the object side of the second lens unit of positiverefractive power is put, so that it is possible to obtain good opticalperformance without increasing the number of constituent lens elements.

[0110] In particular, the zoom lens according to the first embodiment ofthe invention has any one of the following characteristic features(1-1), (1-2) and (1-3) under the basic construction described above.

[0111] (1-1) The first lens unit includes a negative lens of meniscusform having a concave surface facing the image side, and a positive lensof meniscus form having a convex surface facing the object side, and thesecond lens unit includes a cemented lens A of positive refractive poweras a whole disposed on the most image side of the second lens unit andcomposed of a negative lens and a positive lens, and a lens B disposedon the most image side among lenses disposed closer to the object sidethan the cemented lens A, a lens surface on the image side of the lens Bhaving a shape having a concave surface facing the image side.

[0112] In addition, in the above construction (1-1), it is preferable tosatisfy at least one of the following conditions (a-1) and (a-2).

[0113] (a-1) The following conditions are satisfied:

0.5<fc/f2<2.0  (1)

0.5<(Ra+Rb)/(Ra−Rb)<2.5  (2)

[0114] where fc is the focal length of the cemented lens A in the secondlens unit, f2 is the focal length of the second lens unit, Ra is aradius of curvature of a lens surface on the object side of the cementedlens A, and Rb is a radius of curvature of the lens surface on the imageside of the lens B.

[0115] (a-2) The second lens unit includes, in order from the objectside to the image side, a positive lens having a convex surface facingthe object side, a negative lens having a concave surface facing theimage side, and a cemented lens.

[0116] (1-2) The first lens unit includes a negative lens of meniscusform having a concave surface facing the image side, and a positive lensof meniscus form having a convex surface facing the object side, and thesecond lens unit includes a negative lens of bi-concave form, a positivelens disposed on the object side of the negative lens of bi-concave formand having a convex surface facing the object side, and a cemented lensof positive refractive power as a whole disposed on the image side ofthe negative lens of bi-concave form and composed of a negative lens anda positive lens.

[0117] In addition, in the above construction (1-2), it is preferable tosatisfy at least one of the following conditions (b-1) and (b-2).

[0118] (b-1) The following conditions are satisfied:

0.3<|fn|/f2<2.0  (3)

0<(Rd+Rc)/(Rd−Rc)<2.5  (4)

[0119] where fn is the focal length of the negative lens of bi-concaveform in the second lens unit, f2 is the focal length of the second lensunit, Rc and Rd are radii of curvature of lens surfaces on the objectside and the image side, respectively, of the positive lens disposed onthe most object side of the second lens unit and having a convex surfacefacing the object side.

[0120] (b-2) The third lens unit consists of one positive lens, orconsists of a cemented lens of positive refractive power as a wholecomposed of a positive lens and a negative lens.

[0121] (1-3) The first lens unit includes a negative lens of meniscusform having a concave surface facing the image side and a positive lensof meniscus form having a convex surface facing the object side, and thesecond lens unit includes, in order from the object side to the imageside, one or two positive lenses, a negative lens B of bi-concave form,and a cemented lens A composed of a negative lens and a positive lens,and the zoom lens satisfies the following conditions:

0.5<fc/f2<2.0  (1)

0.5<(Ra+Rb)/(Ra−Rb)<2.5  (2)

0.3<|fn|/f2<2.0  (3)

0<(Rd+Rc)/(Rd−Rc)<2.5  (4)

[0122] where fc is the focal length of the cemented lens A in the secondlens unit, f2 is the focal length of the second lens unit, Ra is aradius of curvature of a lens surface on the object side of the cementedlens A, Rb is a radius of curvature of a lens surface on the image sideof the negative lens B, fn is a focal length of the negative lens B inthe second lens unit, Rc and Rd are radii of curvature of lens surfaceson the object side and the image side, respectively, of a positive lensdisposed on the most object side of the second lens unit and having aconvex surface facing the object side.

[0123] Next, the characteristic features of the above constructions(1-1) to (1-3) according to the first embodiment of the invention arefurther described in detail.

[0124] In the zoom lens according to the first embodiment, the firstlens unit of negative refractive power is composed of two lenses, i.e.,in order from the object side to the image side, a negative lens ofmeniscus form having a convex surface facing the object side and apositive lens of meniscus form having a convex surface facing the objectside, or the first lens unit of negative refractive power is composed ofthree lenses, i.e., in order from the object side to the image side, aconcave lens (negative lens) 11 having a concave surface facing theimage side, a concave lens (negative lens) 12 having a concave surfacefacing the image side and a convex lens (positive lens) 13 having aconvex surface facing the object side. Further, the second lens unit ofpositive refractive power is composed of three lens subunits includingfour lens elements, i.e., in order from the object side to the imageside, a convex lens (positive lens) 21 having a convex surface facingthe object side, a concave lens (negative lens) 22 of bi-concave form,and a cemented lens 23 composed of a negative lens and a positive lens,or the second lens unit of positive refractive power is composed of fourlens subunits including five lens elements, i.e., in order from theobject side to the image side, two positive lenses, a negative lens 22of bi-concave form, and a cemented lens 23 composed of a negative lensand a positive lens.

[0125] Further, the third lens unit of positive refractive power iscomposed of one convex lens or a cemented lens composed of a positivelens and a negative lens. By adopting such a desired refractive powerarrangement as to be compatible with the correction of aberrations, asdescribed above, it is possible to attain the compactness of a lenssystem while keeping good optical performance.

[0126] The first lens unit of negative refractive power has the role ofcausing an off-axial principal ray to be pupil-imaged on the center ofthe stop. In particular, since the amount of refraction of the off-axialprincipal ray is large at the wide-angle end, the various off-axialaberrations, particularly, astigmatism and distortion, tend to occur.Therefore, similarly to the ordinary wide-angle lens, the zoom lensaccording to the first embodiment is made to have the concave-convexarrangement by which the increase of the lens diameter on the mostobject side can be prevented, and then the negative refractive power isshared by the two negative lens units 11 and 12 which mainly share thenegative refractive power of the first lens unit. Lenses constitutingthe first lens unit have respective shapes close to concentricalspherical surfaces centered on the center of the stop so as to suppressthe occurrence of off-axial aberration caused by the refraction of anoff-axial principal ray. Thus, each of the negative lenses 11 and 12 ismade in the meniscus form having a concave surface facing the imageside, and the positive lens 13 is made in the meniscus form having aconvex surface facing the object side.

[0127] The second lens unit of positive refractive power is constructedin a symmetrical form on the refractive power arrangement byrespectively disposing positive lenses before and behind the concavelens 22 of bi-concave form. This is because, since the second lens unitis arranged to move greatly during the variation of magnification, inorder to prevent the degradation of optical performance due to thedecentering or the like of lens units caused by a manufacturing error,it is necessary for the second lens unit itself to remove sphericalaberration, coma, etc., to a certain degree.

[0128] The convex lens 21 disposed on the most object side of the secondlens unit is made in a form convex toward the object side so as toprevent an off-axial principal ray having exited from the first lensunit from being greatly refracted to generate the various off-axialaberrations. Further, also, in order to decrease the amount ofoccurrence of spherical aberration with respect to an on-axial lightflux having exited from the first lens unit in a diverging manner, theconvex lens 21 is made in a form convex toward the object side.

[0129] Further, both lens surfaces on the object side and the image sideof the concave lens 22 are concave, and a negative air lens is formed bythe concave lens 22 and each of the convex lens 21 and the positivecemented lens 23 which are disposed before and behind the concave lens22, so that spherical aberration and coma which occur owing to the largeaperture ratio are corrected well.

[0130] Further, the cemented lens 23 is disposed on the image side ofthe concave lens 22 to correct chromatic aberration well. In the zoomlens according to the first embodiment, since the height at which anoff-axial light flux bends in the first lens unit is high at thewide-angle end and low at the telephoto end, the variation of lateralchromatic aberration due to the variation of magnification occurs in thefirst lens unit in particular. Therefore, the refractive powerarrangement of the first lens unit and the selection of glass materialtherefor are made in such a way as to make, especially, the variation oflateral chromatic aberration minimum. In a case where the first lensunit is formed in the concave-convex construction, as described above,to make the first lens unit compact and the number of constituent lenselements of the first lens unit is made to be two or three, a componentof the variation of longitudinal chromatic aberration tends to remainwithin the first lens unit. Therefore, the cemented lens is disposedwithin the second lens unit to correct longitudinal chromatic aberrationwell.

[0131] Further, in order to cause the second lens unit also to take itsshare of the correction of lateral chromatic aberration even to a smallextent, it is effective that the cemented lens is disposed distant fromthe stop. Therefore, in the first embodiment, the cemented lens isdisposed on the image side of the concave lens 22.

[0132] The third lens unit of positive refractive power is constructedwith a convex lens of form having a convex surface facing the objectside, or is constructed with a cemented lens composed of a positive lensand a negative lens, thereby making the image side of the third lensunit telecentric. In addition, the third lens unit is made to serve alsoas a field lens.

[0133] Further, in order to attain the further improvement of opticalperformance while constructing each lens unit with a less number ofconstituent lens elements, an aspheric surface is effectively introducedinto the zoom lens according to the first embodiment.

[0134] In the case of the numerical example 1 shown in FIG. 1, a lenssurface on the image side of the concave lens 11 of the first lens unitis made to be an aspheric surface of such a shape that a divergingfunction becomes progressively weaker toward the marginal portionthereof, thereby correcting curvature of field, astigmatism anddistortion, especially, at the wide-angle side to lower the variation ofaberration due to the variation of magnification.

[0135] Further, a lens surface on the object side of the convex lens 21of the second lens unit is made to be an aspheric surface of such ashape that a converging function becomes progressively weaker toward themarginal portion thereof, thereby effectively correcting sphericalaberration, which becomes conspicuous owing to the large aperture ratio.

[0136] Further, a lens surface on the object side of the convex lens 31of the third lens unit is made to be an aspheric surface of such a shapethat a converging function becomes progressively weaker toward themarginal portion thereof, thereby effectively correcting curvature offield, astigmatism and distortion in the whole range of the variation ofmagnification.

[0137] In a case where a near-distance object is photographed by usingthe zoom lens according to the first embodiment, good focusingperformance can be obtained by moving the first lens unit toward theobject side. However, the rear-focusing method in which the third lensunit is moved toward the object side for focusing may be employed. Thismethod gives the advantage of preventing the diameter of a front lensmember from increasing due to focusing, the advantage of shortening theminimum imaging distance, and the advantage of lightening the focusinglens unit.

[0138] Next, the technical significance of each of the above-mentionedconditions (1) to (4) is described.

[0139] The condition (1) is an inequality for regulating the refractivepower of the cemented lens of the second lens unit. The second lens unitin the first embodiment takes the symmetrical refractive powerarrangement of positive, negative and positive refractive powers, asmentioned in the foregoing. The refractive power of the cemented lensbears the positive refractive power on the image side of the second lensunit. Therefore, it is desirable that the refractive power of thecemented lens lies within a certain range compared with the refractivepower of the second lens unit.

[0140] If the refractive power of the cemented lens becomes weakerbeyond the upper limit of the condition (1), it becomes necessary tostrengthen the refractive power of the positive lens oh the object sideof the second lens unit to make the second lens unit have a necessaryconverging function. In this instance, excessive spherical aberrationoccurs, the correction of which would become insufficient even if anaspheric surface is used. If the refractive power of the positive lenson the object side of the second lens unit is not strengthened, therefractive power of the second lens unit itself becomes weaker.Therefore, the amount of movement for the variation of magnificationbecomes large, causing an increase of the total lens length and thediameter of a front lens member, so that it becomes impossible toconstruct a compact zoom lens.

[0141] On the other hand, if the refractive power of the cemented lensbecomes stronger beyond the lower limit of the condition (1), thePetzval sum in the second lens unit becomes large in the positivedirection, causing curvature of field in the under direction. Further,in order to correct longitudinal chromatic aberration, it is necessaryto make the curvature of the cementing surface of the cemented lensstronger. Accordingly, in order to secure the edge thickness of thepositive lens of the cemented lens, the lens thickness at the centralportion of the cemented lens has to be made larger. This isdisadvantageous in compactness of the zoom lens.

[0142] The condition (2) is an inequality for defining the shape factorof an air lens of negative refractive power which is formed by thecemented lens disposed on the image side of the second lens unit and theconcave lens disposed immediately before the cemented lens.

[0143] If the stop is disposed on the object side of the second lensunit, coma of the same sign is caused by a lens surface on the objectside of the positive lens disposed on the object side of the second lensunit and a lens surface on the object side of the concave lens of thesecond lens unit. On the other hand, coma of the sign different from theabove sign is caused by a lens surface on the object side of the airlens, and coma of the same sign as the above sign is caused by a lenssurface on the image side of the air lens. Therefore, if the curvatureof the lens surface on the object side of the air lens is made strong toa certain extent in the form of a concave surface facing the image sideand, on the other hand, the curvature of the lens surface on the imageside of the air lens is made relatively weak, coma is effectivelycorrected. Incidentally, when the shape factor in the condition (2) islarger than “1”, the air lens takes the meniscus form, and, when smallerthan _(“)1”, the air lens is a bi-convex lens. As the shape factorbecomes larger from “1”, the lens surface on the image side of the airlens has a smaller radius of curvature while having the center ofcurvature thereof on the image side, and, on the other hand, as theshape factor becomes smaller from “1”, the lens surface on the imageside of the air lens has a smaller radius of curvature while having thecenter of curvature thereof on the object side.

[0144] If the degree of meniscus form of the air lens is strengthenedbeyond the upper limit of the condition (2), the curvature of the lenssurface on the image side of the air lens becomes too strong, so thatthe faculty of the air lens for correcting coma becomes weak. As aresult, coma is insufficiently corrected by the second lens unit.

[0145] If the shape factor of the air lens becomes smaller than “1”, thelens surface on the image side of the air lens has the center ofcurvature thereof on the object side, so that the air lens takes thebi-convex form. Accordingly, the cemented lens, which is disposed on theimage side of the air lens, takes the meniscus form. Then, in order tomake the cemented lens have such a refractive power as to satisfy thecondition (1), it is necessary to strengthen the curvature of the lenssurface on the image side of the cemented lens. If the lower limit ofthe condition (2) is exceeded, as a result, the curvature of the lenssurface on the image side of the cemented lens becomes too strong, sothat spherical aberration in the under direction occurs, which is notsufficiently corrected even by using an aspheric surface.

[0146] The condition (3) is an inequality for regulating a refractivepower of the negative lens of bi-concave form of the second lens unit.

[0147] If the refractive power of the negative lens becomes weak beyondthe upper limit of the condition (3), the Petzval sum in the second lensunit increases in the positive direction, thereby causing curvature offield in the under direction. Further, it becomes impossible to secure asufficient back focal distance for disposing a filter or the like.Furthermore, a problem arises in that it is impossible to make the exitpupil sufficiently distant from the image plane.

[0148] If the refractive power of the negative lens becomes strongbeyond the lower limit of the condition (3), spherical aberration isover-corrected, curvature of field occurs in the over direction, and theback focal distance becomes too long to make the zoom lens compact.

[0149] The condition (4) is an inequality for defining the shape factorof the positive lens on the object side of the second lens unit.

[0150] If the curvature of the lens surface on the image side of thepositive lens becomes strong while having the center of curvaturethereof on the image side beyond the upper limit of the condition (4),in particular, coma occurs conspicuously, which is difficult to correcteven by using an aspheric surface.

[0151] If the curvature of the lens surface on the image side of thepositive lens becomes strong while having the center of curvaturethereof on the object side™ beyond the lower limit of the condition (4),the angle of incidence of an on-axial land ray on the lens surface onthe image side of the positive lens becomes too large, so that sphericalaberration occurs in the under direction.

[0152] Next, numerical data of the numerical examples 1 to 5 of theinvention are shown. In the numerical data of the numerical examples 1to 5, Ri denotes the radius of curvature of the i-th surface, whencounted from the object side, Di denotes the lens thickness or airseparation between the i-th surface and the (i+1)th surface, whencounted from the object side, Ni and νi respectively denote therefractive index and Abbe number, relative to d-line, of the i-thoptical member, when counted from the object side. Further, the twosurfaces closest to the image side constitute a filter member, such as acrystal low-pass filter or an infrared cutting filter.

[0153] The shape of an aspheric surface is expressed in the coordinateswith an X axis in the optical axis direction and an H axis in thedirection perpendicular to the optical axis, the direction in whichlight advances being taken as positive, by the following equation:$X = {\frac{\left( {1/R} \right)H^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)\left( {H/R} \right)^{2}}}} + {BH}^{4} + {CH}^{6} + {DH}^{8} + {EH}^{10} + {FH}^{12}}$

[0154] where R is the radius of osculating sphere, and K, B, C, D, E andF are aspheric coefficients. Further, the indication “e-0×” means“×10^(-x)”.

[0155] In addition, the values of the factors in the above-mentionedconditions (1) to (4) for the numerical examples 1 to 5 are listed inTable-1.

NUMERICAL EXAMPLE 1

[0156] The zoom lens according to the numerical example 1 is constructedwith, in order from the object side to the image side, a first lens unitof negative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side. Lens data of the numerical example 1 isshown as follows.

NUMERICAL EXAMPLE 1

[0157] f = 1.00 − 1.99  Fno = 2.90 − 4.12  2ω = 68.6° − 36.8° R1 = 7.468D1 = 0.21 N1 = 1.674700 ν1 = 54.9 R2 = 0.993* D2 = 0.21 R3 = 2.407 D3 =0.10 N2 = 1.728250 ν2 = 28.5 R4 = 1.188 D4 = 0.19 R5 = 1.486 D5 = 0.32N3 = 1.846660 ν3 = 23.8 R6 = 5.074 D6 = Variable R7 = Stop D7 = 0.00 R8= 0.981* D8 = 0.38 N4 = 1.693500 ν4 = 53.2 R9 = −4.331 D9 = 0.04 R10 =−1.864 D10 = 0.14 N5 = 1.516330 ν5 = 64.1 R11 = 0.906 D11 = 0.13 R12 =17.071 D12 = 0.08 N6 = 1.846660 ν6 = 23.8 R13 = 0.966 D13 = 0.35 N7 =1.772499 ν7 = 49.6 R14 = −1.646 D14 = Variable R15 = 2.410* D15 = 0.25N8 = 1.583130 ν8 = 59.5 R16 = −38.921 D16 = Variable R17 = ∞ D17 = 0.43N9 = 1.544270 ν9 = 70.6 R18 = ∞

[0158] Variable Focal Length Separation 1.00 1.50 1.99 D6 1.88 0.80 0.41D14 0.77 1.43 2.34 D16 0.60 0.58 0.32

[0159] Aspheric Coefficients: R2 K = 0 B = −1.23832e−01 C =−2.29538e−02D = −2.45611e−01 E = 3.31822e−01 F = −2.96505e−01 R8 K = 0 B =−5.79780e−02 C = −1.08652e−02 D = 2.34725e−02 E = 2.63031e−01 F =0.00000e+00 R15 K =0 B = 5.91674e−04 C = −5.06821e−02 D = 2.87149e−01 E= −5.94448e−01 F = 4.55368e−01

NUMERICAL EXAMPLE 2

[0160] The zoom lens according to the numerical example 2 is constructedwith, in order from the object side to the image side, a first lens unitof negative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side. Lens data of the numerical example 2 isshown as follows.

NUMERICAL EXAMPLE 2

[0161] f = 1.00-2.54  Fno = 2.89-4.60  2ω = 70.2°-28.0° R1 = 7.492 D1 =0.21 N1 = 1.674700 ν1 = 54.9 R2 = 1.121* D2 = 0.30 R3 = −7.375 D3 = 0.13N2 = 1.720000 ν2 = 43.7 R4 = 3.048 D4 = 0.19 R5 = 2.496 D5 = 0.27 N3 =1.846660 ν3 = 23.8 R6 = 13.429 D6 = Variable R7 = Stop D7 = 0.00 R8 =1.142* D8 = 0.32 N4 = 1.693500 ν4 = 53.2 R9 = −21.428 D9 = 0.03 R10 =−3.947 D10 = 0.22 N5 = 1.517417 ν5 = 52.4 R11 = 1.061 D11 = 0.08 R12 =2.860 D12 = 0.08 N6 = 1.846660 ν6 = 23.8 R13 = 1.004 D13 = 0.32 N7 =1.772499 ν7 = 49.6 R14 = −2.683 D14 = Variable R15 = 2.498* D15 = 0.29N8 = 1.583130 ν8 = 59.5 R16 = −31.782 D16 = Variable R17 = ∞ D17 = 0.43N9 = 1.544270 ν9 = 70.6 R18 = ∞

[0162] Variable Focal Length Separation 1.00 1.76 2.54 D6 2.04 0.77 0.25D14 1.69 2.69 3.68 D16 0.26 0.21 0.16

[0163] Aspheric Coefficients: R2 K = 0 B = −3.92457e−02 C = 1.76441e−02D = −1.79210e−01 E = 3.23743e−01 F = −2.57814e−01 R8 K = 0 B =−4.52188e−02 C = −7.37087e−03 D = 0.00000e+00 E = 0.00000e+00 F =0.00000e+00 R15 K = 0 B = −1.06457e−01 C = 2.32651e−01 D = −1.16441e+00E = 2.17741e+00 F = −1.56135e+00

NUMERICAL EXAMPLE 3

[0164] The zoom lens according to the numerical example 3 is constructedwith, in order from the object side to the image side, a first lens unitof negative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side.

[0165] The numerical example 3 differs from the numerical example 1 inthat the number of constituent lens elements of the first lens unit istwo. In the numerical example 3, the first lens unit is constructed witha negative lens of meniscus form having a concave surface facing theimage side and a positive lens of meniscus form having a convex surfacefacing the object side, that is, two concave lenses in the numericalexample 1 are formed into one concave lens. This arrangement gives suchadvantages that the number of lens elements is reduced to lead toreduction in cost, and the front lens member is reduced in weight. Lensdata of the numerical example 3 is shown as follows.

NUMERICAL EXAMPLE 3

[0166] f = 1.00-2.00  Fno = 2.49-3.50  2ω = 70.2°-37.6° R1 = 15.872 D1 =0.21 N1 = 1.674700 ν1 = 54.9 R2 = 0.984* D2 = 0.51 R3 = 2.011 D3 = 0.25N2 = 1.846660 ν2 = 23.8 R4 = 3.882 D4 = Variable R5 = Stop D5 = 0.00 R6= 1.049* D6 = 0.38 N3 = 1.693500 ν3 = 53.2 R7 = −18.496 D7 = 0.06 R8 =−1.875 D8 = 0.14 N4 = 1.522494 ν4 = 59.8 R9 = 1.019 D9 = 0.10 R10 =7.075 D10 = 0.08 N5 = 1.805181 ν5 = 25.4 R11 = 0.879 D11 = 0.35 N6 =1.772499 ν6 = 49.6 R12 = −1.696 D12 = Variable R13 = 2.412* D13 = 0.25N7 = 1.583130 ν7 = 59.5 R14 = −39.003 D14 = Variable R15 = ∞ D15 = 0.43N8 = 1.544270 ν8 = 70.6 R16 = ∞

[0167] Variable Focal Length Separation 1.00 1.52 2.00 D4 2.12 0.84 0.41D12 0.79 1.45 2.35 D14 0.59 0.57 0.32

[0168] Aspheric Coefficients: R2 K = 0 B = −1.14032e−01 C = 2.67387e−02D = −3.23821e−01 E = 4.20448e−01 F = −3.39683e−01 R6 K = 0 B =−3.07051e−02 C = 2.68063e−02 D = 0.00000e+00 E = 0.00000e+00 F =0.00000e+00 R13 K = 0 B = −2.75565e−02 C = 1.56521e−01 D = −5.60681e−01E = 1.06327e+00 F = −7.73626e−01

NUMERICAL EXAMPLE 4

[0169] The zoom lens according to the numerical example 4 is constructedwith, in order from the object side to the image side, a first lens unitof negative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side.

[0170] The numerical example 4 differs from the numerical example 1 inthat the number of constituent lens elements of the second lens unit isfive, being grouped into four lens subunits. In the numerical example 4,the second lens unit is constructed with, in order from the object sideto the image side, a positive lens of meniscus form having a convexsurface facing the object side, a convex lens of bi-convex form, aconcave lens of bi-concave form, and a cemented lens of positiverefractive power as a whole composed of a concave lens and a convexlens, that is, one positive lens on the object side in the numericalexample 1 is formed into two positive lenses. This arrangement enablesthe two positive lenses to share the function of converging an on-axiallight flux which has exited from the first lens unit in a divergingstate, and, therefore, gives such advantages that it is possible toreduce the occurrence of spherical aberration and it is possible toconstruct a photographic lens having a larger aperture diameter. Lensdata of the numerical example 4 is shown as follows.

NUMERICAL EXAMPLE 4

[0171] f = 1.00-2.00  Fno = 2.00-3.00  2ω = 66.0° -35.2° R1 = 7.477 D1 =0.21 N1 = 1.674700 ν1 = 54.9 R2 = 1.046* D2 = 0.20 R3 = 2.556 D3 = 0.10N2 = 1.728250 ν2 = 28.5 R4 = 1.145 D4 = 0.19 R5 = 1.463 D5 = 0.27 N3 =1.846660 ν3 = 23.8 R6 = 4.613 D6 = Variable R7 = Stop D7 = 0.00 R8 =1.381 D8 = 0.25 N4 = 1.693500 ν4 = 53.2 R9 = 6.370 D9 = 0.03 R10 =1.615* D10 = 0.29 N5 = 1.693500 ν5 = 53.2 R11 = −4.778 D11 = 0.04 R12 =−2.130 D12 = 0.14 N6 = 1.516330 ν6 = 64.1 R13 = 0.907 D13 = 0.14 R14 =−70.592 D14 = 0.08 N7 = 1.846660 ν7 = 23.8 R15 = 0.990 D15 = 0.35 N8 =1.772499 ν8 = 49.6 R16 = −1.991 D16 = Variable R17 = 1.819* D17 = 0.29N9 = 1.583130 ν9 = 59.5 R18 = −38.968 D18 = Variable R19 = ∞ D19 = 0.43N10 = 1.544270 ν10 = 70.6 R20 = ∞

[0172] Variable Focal Length Separation 1.00 1.49 2.00 D6 1.88 0.92 0.41D16 0.91 1.59 2.26 D18 0.39 0.35 0.32

[0173] Aspheric Coefficients: R2 K = 0 B = −1.13188e−01 C = 1.50616e−04D = −2.51746e−01 E = 3.47476e−01 F = −2.63121e−01 R10 K = 0 B =−2.71823e−02 C = 2.14414e−02 D = −2.52640e−02 E = 0.00000e+00 F =0.00000e+00 R17 K = 0 B = −3.50857e−02 C = 3.08965e−02 D = 1.84237e−01 E= −6.40556e−01 F = 5.97621e−01

NUMERICAL EXAMPLE 5

[0174] The zoom lens according to the numerical example 5 is constructedwith, in order from the object side to the image side, a first lens unitof negative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitremains stationary.

[0175] The numerical example 5 differs from the numerical example 1 inthat the number of constituent lens elements of the third lens unit istwo, being grouped into one lens subunit. In the numerical example 5,the third lens unit is constructed with a cemented lens of positiverefractive power as a whole composed of a convex lens and a concavelens, that is, a single lens in the numerical example 1 is formed into acemented lens. This arrangement enables lateral chromatic aberration, inparticular, to be corrected by the third lens unit. As mentioned in theforegoing, the variation of lateral chromatic aberration due to zoomingis caused greatly by the first lens unit. However, in the case of thenumerical example 5, the correction of lateral chromatic aberration canbe shared such that the component of the variation of lateral chromaticaberration is corrected by the first lens unit and the absolute amountof lateral chromatic aberration is corrected by the third lens unit.Accordingly, the numerical example 5 has such advantages that it ispossible to correct lateral chromatic aberration well over the wholerange of the variation of magnification even when the zoom ratio isincreased.

[0176] Further, the numerical example 5 differs from the numericalexample 1 in that the third lens unit remains stationary during zooming.With the third lens unit kept stationary, the numerical example 5 hassuch advantages that, since any moving mechanism for the third lens unitis not necessary, the construction of a lens barrel can be simplified.Lens data of the numerical example 5 is shown as follows.

NUMERICAL EXAMPLE 5

[0177] f = 1.00-2.98  Fno = 2.78-4.60  2ω = 70.0°-23.8° R1 = 7.471 D1 =0.21 N1 = 1.674700 ν1 = 54.9 R2 = 1.392* D2 = 0.29 R3 = −8.099 D3 = 0.13N2 = 1.723420 ν2 = 38.0 R4 = 1.731 D4 = 0.19 R5 = 2.191 D5 = 0.32 N3 =1.846660 ν3 = 23.8 R6 = 137.077 D6 = Variable R7 = Stop D7 = 0.00 R8 =1.335* D8 = 0.38 N4 = 1.693500 ν4 = 53.2 R9 = −5.330 D9 = 0.05 R10 =−2.015 D10 = 0.14 N5 = 1.517417 ν5 = 52.4 R11 = 1.319 D11 = 0.08 R12 =7.466 D12 = 0.08 N6 = 1.846660 ν6 = 23.8 R13 = 1.351 D13 = 0.35 N7 =1.772499 ν7 = 49.6 R14 = −1.958 D14 = Variable R15 = 2.272* D15 = 0.27N8 = 1.583130 ν8 = 59.5 R16 = −7.923 D16 = 0.08 N9 = 1.698947 ν9 = 30.1R17 = −31.691 D17 = 0.08 R18 = ∞ D18 = 0.43 N10 = 1.544270 ν10 = 70.6R19 = ∞

[0178] Variable Focal Length Separation 1.00 1.99 2.98 D6 2.92 0.92 0.25D14 2.17 3.41 4.64

[0179] Aspheric Coefficients: R2 K = 0 B = −3.90048e−02 C = 8.55478e−02D = −3.52446e−01 E = 5.28091e−01 F = −2.97792e−01 R8 K = 0 B =−2.41197e−02 C = 1.74507e−02 D = 0.00000e+00 E = 0.00000e+00 F =0.00000e+00 R15 K = 0 B = −5.30968e−02 C = −9.80294e−02 D = 1.70223e−01E = −2.85852e−01 F = 1.85253e−01

[0180] TABLE 1 Numerical Example Condition 1 2 3 4 5 (1) 1.11 1.04 0.881.64 1.00 (2) 1.11 2.18 1.34 0.97 1.43 (3) 0.57 0.82 0.57 0.61 0.68 (4)0.63 0.90 0.89 1.55 0.60

[0181] According to the first embodiment of the invention, it ispossible to attain a zoom lens which is suited for a photographic systemusing a solid-state image sensor, has a high variable magnificationratio despite being compact and small in diameter with less constituentlens elements, is corrected particularly for chromatic aberration, andhas excellent optical performance.

[0182] (Second Embodiment)

[0183]FIG. 21 to FIGS. 32A to 32D relate to a second embodiment of theinvention, which corresponds to numerical examples 6 to 8 of theinvention to be described later.

[0184]FIG. 21 is a lens block diagram showing a zoom lens according tothe numerical example 6 of the invention. FIGS. 22A to 22D through FIGS.24A to 24D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 6 of the invention.

[0185]FIG. 25 is a lens block diagram showing a zoom lens according tothe numerical example 7 of the invention. FIGS. 26A to 26D through FIGS.28A to 28D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 7 of the invention.

[0186]FIG. 29 is a lens block diagram showing a zoom lens according tothe numerical example 8 of the invention. FIGS. 30A to 30D through FIGS.32A to 32D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 8 of the invention.

[0187] In the lens block diagrams shown in FIGS. 21, 25 and 29,reference character L1 denotes a first lens unit of negative refractivepower, reference character L2 denotes a second lens unit of positiverefractive power, reference character L3 denotes a third lens unit ofpositive refractive power, reference character SP denotes an aperturestop for determining the rightness of an optical system, referencecharacter IP denotes an image plane, and reference character G denotes aglass block, such as a filter or a color separation prism.

[0188] The zoom lens according to the second embodiment has three lensunits, i.e., in order from the object side to the image side, the firstlens unit L1 of negative refractive power, the second lens unit L2 ofpositive refractive power and the third lens unit L3 of positiverefractive power. During zooming from the wide-angle end to thetelephoto end, the first lens unit makes a reciprocating motion convextoward the image side, the second lens unit moves toward the objectside, and the third lens unit moves toward the image side or moves witha locus convex toward the image side.

[0189] In the zoom lens according to the second embodiment, thevariation of magnification is effected mainly by moving the second lensunit while the shift of an image point due to the variation ofmagnification is compensated for by moving forward and backward thefirst lens unit and moving the third lens unit toward the image side ormoving the third lens unit with a locus convex toward the image side.

[0190] The third lens unit shares the increase of a refractive power ofthe photographic lens due to the reduction in size of the image sensor,thereby reducing a refractive power of the short zoom system composed ofthe first and second lens units, so that the occurrence of aberration bylenses constituting the first lens unit can be suppressed, so as toattain high optical performance. Further, the telecentric imageformation on the image side necessary for the photographing apparatus(optical apparatus) using the image sensor or the like is attained bygiving the third lens unit the roll of a field lens.

[0191] Further, the stop SP is disposed on the most object side of thesecond lens unit, thereby shortening the distance between the entrancepupil and the first lens unit on the wide-angle side, so that theincrease of the diameter of lenses constituting the first lens unit canbe prevented. In addition, the various off-axial aberrations arecanceled by the first lens unit and the third lens unit across the stopdisposed on the object side of the second lens unit, so that goodoptical performance can be obtained without increasing the number ofconstituent lenses.

[0192] The zoom lens according to the second embodiment is characterizedin that the first lens unit has one negative lens and one positive lens,the second lens unit is composed of one cemented lens and a positivelens, and the third lens unit is has at least one positive lens.

[0193] As has been described in the foregoing, according to the secondembodiment, the first lens unit of negative refractive power is composedof two lenses, i.e., in order from the object side to the image side, anegative lens 11 having a concave surface facing the image side, and apositive lens 12 of meniscus form having a convex surface facing theobject side, the second lens unit of positive refractive power iscomposed of three lenses as a whole, i.e., a positive lens 21 ofbi-convex form, a negative lens 22 having a concave surface facing theobject side, and a positive lens 23 of bi-convex form, two of the threelenses constituting a cemented lens, and the third lens unit of positiverefractive power is composed of a single positive lens 31 having aconvex surface facing the object side.

[0194] With the respective lens units having such a lens construction asto make the desired refractive power arrangement and the correction ofaberration compatible with each other, as described above, it ispossible to attain the compactness of a lens system while keeping thegood optical performance of the lens system. The first lens unit ofnegative refractive power has the role of causing an off-axial principalray to be pupil-imaged on the center of a stop, and, particularly, onthe wide-angle side, the amount of refraction of an off-axial principalray is large. Therefore, in the first lens unit, the various off-axialaberrations, particularly, astigmatism and distortion, are apt to occur.Accordingly, similarly to an ordinary wide-angle lens, the first lensunit is made to have the construction having a negative lens and apositive lens so as to prevent the diameter of a lens disposed on themost object side from increasing. Further, it is preferable that a lenssurface on the image side of the negative lens 11 is such an asphericsurface that a negative refractive power becomes progressively weakertoward a marginal portion of the lens surface. By this arrangement,astigmatism and distortion are corrected in a well-balanced manner, andthe first lens unit is composed of such a small number of lenses as two,so that it becomes easy to make the entire lens system compact. Inaddition, in order to prevent the occurrence of an off-axial aberrationdue to the refraction of an off-axial principal ray, each of lensesconstituting the first lens unit has a lens surface approximate toconcentric spherical surfaces having the center on a point at which thestop and the optical axis intersect.

[0195] The second lens unit of positive refractive power has thepositive lens 21 of bi-convex form disposed on the most object side ofthe second lens unit, so that the second lens unit has such a shape asto lessen the angle of refraction of an off-axial principal ray havingexited from the first lens unit, thereby preventing the variousoff-axial aberrations from occurring. Further, the positive lens 21 is alens arranged to allow an on-axial ray to pass at the largest height,and is concerned with the correction of, mainly, spherical aberrationand coma. In the second embodiment, it is preferable that a lens surfaceon the object side of the positive lens 21 is such an aspheric surfacethat a positive refractive power becomes progressively weaker toward amarginal portion of the lens surface. By this arrangement, it becomeseasy to correct well spherical aberration and coma.

[0196] In the zoom lens according to the numerical example 6 shown inFIG. 21, the negative lens 22 disposed on the image side of the positivelens 21 is made to have a concave surface facing the object side, sothat a negative air lens is formed by the lens surface on the image sideof the positive lens 21 and the concave surface on the object side ofthe negative lens 22. Accordingly, it is possible to correct sphericalaberration occurring due to the increase of an aperture ratio.

[0197] Further, in the zoom lenses according to the numerical examples 6and 7 shown in FIGS. 21 and 25, it is preferable that a lens surface onthe image side of the positive lens 23 disposed on the most image sideof the second lens unit L2 is such an aspheric surface that a positiverefractive power becomes progressively stronger toward a marginalportion of the lens surface. By this arrangement, it is possible toeffectively correct spherical aberration, which becomes conspicuous dueto the increase of an aperture ratio.

[0198] In addition, in the second embodiment, in order to cope with thereduction of the amount of chromatic aberration, which is requiredaccording to the increased number of pixels and the minimization of cellpitches of a solid-state image sensor such as a CCD, a cemented lenscomposed of a negative lens and a positive lens cemented together isdisposed in the second lens unit. By this arrangement, it is possible tocorrect well longitudinal chromatic aberration and lateral chromaticaberration.

[0199] The third lens unit of positive refractive power has a convexlens (positive lens) 31 having a convex surface facing the object side,and serves also as a field lens for making the zoom lens telecentric onthe image side. Further, a lens surface on the image side of the convexlens 31 is such an aspheric surface that a positive refractive powerbecomes progressively weaker toward a marginal portion of the lenssurface, and contributes to the correction of the various off-axialaberrations over the entire zooming range. Now, when the back focaldistance is denoted by sk′, the focal length of the third lens unit isdenoted by f3, and the image magnification of the third lens unit isdenoted by β3, the following relation is obtained:

sk′=f3 (1−β3)

[0200] provided that 0<β3<1.0. Here, when the third lens unit is movedtoward the image side during the variation of magnification from thewide-angle end to the telephoto end, the back focal distance sk′decreases, so that the image magnification β3 of the third lens unitincreases on the telephoto side. Then, as a result, the third lens unitshares the variation of magnification with the second lens unit, so thatthe amount of movement of the second lens unit is reduced. Therefore,since such a space for the movement of the second lens unit can besaved, the third lens unit contributes to the reduction in size of thelens system.

[0201] When a close-distance object is to be photographed by using thezoom lens according to the second embodiment, the good opticalperformance can be obtained by moving the first lens unit toward theobject side. However, it is preferable to move the third lens unit alsotoward the object side. This arrangement prevents the increase of thediameter of a front lens member due to the focusing movement of thefirst lens unit which is disposed on the most object side, prevents theincrease of the load on an actuator for moving the first lens unit whichis the heaviest among the lens units, and makes it possible to move,during zooming, the first lens unit and the second lens unit in aninterlocking relation simply with a cam or the like used. Therefore, itis possible to attain the simplification of a mechanism and theenhancement of precision thereof.

[0202] Further, in a case where focusing is performed by using the thirdlens unit, if the third lens unit is arranged to be moved toward theimage side during the variation of magnification from the wide-angle endto the telephoto end, the telephoto end, at which the amount of movementfor focusing is large, can be located on the image side. Accordingly, itbecomes possible to minimize the amount of total movement of the thirdlens unit required for zooming and focusing. This arrangement makes itpossible to attain the compactness of the entire lens system.

[0203] Further, according to the second embodiment, it is morepreferable to satisfy at least one of the following conditions (c-1) to(c-4).

[0204] (c-1) The following conditions are satisfied:

nd<1.8  (5)

νd<40  (6)

[0205] where nd and νd are a refractive index and Abbe number,respectively, of material of the negative lens included in the secondlens unit.

[0206] If the upper limit of the condition (5) is exceeded, the Petzvalsum increases in the positive direction, so that it becomes difficult tocorrect curvature of field. If the upper limit of the condition (6) isexceeded, it becomes disadvantageously difficult to correct longitudinalchromatic aberration at the telephoto end.

[0207] (c-2) The following condition is satisfied:

0.1<|X1/X3|<7.0  (7)

[0208] where X1 is a distance on the optical axis between a position atwhich the first lens unit is located on the most object side and aposition at which the first lens unit is located on the most image sideduring the variation of magnification from the wide-angle end to thetelephoto end, and X3 is a distance on the optical axis between aposition at which the third lens unit is located on the most object sideand a position at which the third lens unit is located on the most imageside during the variation of magnification from the wide-angle end tothe telephoto end when an object distance is infinity.

[0209] The condition (7) is provided for shortening the total length ofthe optical system and for shortening the total length of the entirelens system obtained when the lens system is retracted.

[0210] Here, the distance X1 is the total stroke of the first lens unitduring the variation of magnification from the wide-angle end to thetelephoto end, and the distance X3 is the total stroke of the third lensunit during the variation of magnification from the wide-angle end tothe telephoto end when an object distance is infinity.

[0211] If the lower limit of the condition (7) is exceeded, the amountof movement of the third lens unit on the optical axis increases, and itbecomes necessary to lengthen the motor shaft for moving the third lensunit, so that it becomes disadvantageously difficult to shorten thetotal length of the lens system as retracted. If the upper limit of thecondition (7) is exceeded, the locus of the first lens unit convextoward the image side becomes sharp, and the angle of a cam locus forthe first lens unit leading from the wide-angle end to the telephoto endbecomes large, so that the total length of the lens system as retractedis caused to become large disadvantageously.

[0212] (c-3) The following condition is satisfied:

0.25<(DL1+DL2+DL3)/DL<0.45  (8)

[0213] where DL is a distance, at the telephoto end, from a vertex onthe object side of a lens disposed on the most object side of the firstlens unit to an image plane, DL1 is a distance from the vertex on theobject side of the lens disposed on the most object side of the firstlens unit to a vertex on the image side of a lens disposed on the mostimage side of the first lens unit, DL2 is a distance from a vertex-onthe object side of a lens disposed on the most object side of the secondlens unit to a vertex on the image side of a lens disposed on the mostimage side of the second lens unit, and DL3 is a distance from a vertexon the object side of a lens disposed on the most object side of thethird lens unit to a vertex on the image side of a lens disposed on themost image side of the third lens unit.

[0214] The condition (8) is provided for shortening the total length ofthe optical system and for shortening the total length of the entirelens system obtained when the lens system is retracted.

[0215] If the upper limit of the condition (8) is exceeded, although thetotal length of the optical system at the telephoto end becomes short,the sum of lengths of the respective lens units on the optical axisbecomes large, so that the total length of the entire lens system asretracted becomes long disadvantageously. If the lower limit of thecondition (8) is exceeded, although the sum of lengths of the respectivelens units on the optical axis becomes small, the total length of theoptical system at the telephoto end becomes long, and the amount ofmovement of each lens unit is necessarily increased. Therefore, thelength of a cam ring or the like for moving each lens unit becomes long,and, as a result, the total length of the entire lens system asretracted does not become short.

[0216] (c-4) The following condition is satisfied:

0.02<DA2/DD2<0.25  (9)

[0217] where DD2 is the sum of thicknesses on the optical axis of lensesconstituting the second lens unit, and DA2 is the sum of air separationsincluded in the second lens unit.

[0218] The condition (9) is provided for making the compactness of theoptical system and the attainment of good optical performance compatiblewith each other.

[0219] If the upper limit of the condition (9) is exceeded, the lengthof the second lens unit on the optical axis becomes long, so that itbecomes disadvantageously difficult to attain the compactness of theoptical system. If the lower limit of the condition (9) is exceeded, thepower of the air lens becomes small, so that it becomesdisadvantageously difficult to correct spherical aberration.

[0220] Next, the concrete lens construction of each of the zoom lensesaccording to the numerical examples 6 to 8 is described.

NUMERICAL EXAMPLE 6

[0221] The zoom lens according to the numerical example 6 is a zoom lenshaving the variable magnification ratio of about 2 and the apertureratio of 2.9-4.0 or thereabout. FIG. 21 shows an optical sectional viewof the zoom lens according to the numerical example 6.

[0222] In the numerical example 6 shown in FIG. 21, the first lens unitof negative refractive power is composed of two lenses, i.e., in orderfrom the object side to the image side, a negative lens 11 of meniscusform having a concave surface facing the image side, and a positive lens12 of meniscus form having a convex surface facing the object side.

[0223] The second lens unit of positive refractive power is composed ofthree lenses as a whole, i.e., in order from the object side to theimage side, a positive lens 21 of bi-convex form, a negative lens 22 ofbi-concave form, and a positive lens 23 of bi-convex form, and thenegative lens 22 and the positive lens 23 constitute a cemented lens.Further, the third lens unit of positive refractive power is composed ofa positive lens 31 having a convex surface facing the object side.

[0224] Further, during zooming from the wide-angle end to the telephotoend, the first lens unit makes a reciprocating motion convex toward theimage side, the second lens unit moves toward the object side, and thethird lens unit moves with a locus convex toward the image side.

NUMERICAL EXAMPLE 7

[0225] The zoom lens according to the numerical example 7 is a zoom lenshaving the variable magnification ratio of about 2 and the apertureratio of 2.7-4.0 or thereabout. FIG. 25 shows an optical sectional viewof the zoom lens according to the numerical example 7.

[0226] In the numerical example 7 shown in FIG. 25, the first lens unitof negative refractive power is composed of two lenses, i.e., in orderfrom the object side to the image side, a negative lens 11 of meniscusform having a concave surface facing the image side, and a positive lens12 of meniscus form having a convex surface facing the object side.

[0227] The second lens unit of positive refractive power is composed ofthree lenses as a whole, i.e., in order from the object side to theimage side, a positive lens 21 of bi-convex form, a negative lens 22 ofbi-concave form, and a positive lens 23 of bi-convex form, and thepositive lens 21 and the negative lens 22 constitute a cemented lens.Further, the third lens unit of positive refractive power is composed ofa positive lens 31 of bi-convex form.

[0228] Further, during zooming from the wide-angle end to the telephotoend, the first lens unit makes a reciprocating motion convex toward theimage side, the second lens unit moves toward the object side, and thethird lens unit moves with a locus convex toward the image side.

NUMERICAL EXAMPLE 8

[0229] The zoom lens according to the numerical example 8 is a zoom lenshaving the variable magnification ratio of about 2 and the apertureratio of 2.8-4.0 or thereabout. FIG. 29 shows an optical sectional viewof the zoom lens according to the numerical example 8.

[0230] In the numerical example 8 shown in FIG. 29, the first lens unitof negative refractive power is composed of two lenses, i.e., in orderfrom the object side to the image side, a negative lens 11 of bi-concaveform, and a positive lens 12 of meniscus form having a convex surfacefacing the object side.

[0231] The second lens unit of positive refractive power is composed ofthree lenses as a whole, i.e., in order from the object side to theimage side, a positive lens 21 of bi-convex form, a positive lens 22 ofbi-convex form, and a negative lens 23 of bi-concave form, and thepositive lens 22 and the negative lens 23 constitute a cemented lens.Further, the third lens unit of positive refractive power is composed ofa positive lens 31 of bi-convex form.

[0232] Further, during zooming from the wide-angle end to the telephotoend, the first lens unit moves toward the object side, the second lensunit also moves toward the object side, and the third lens unit moveswith a locus convex toward the image side.

[0233] According to the second embodiment, with the respective lenselements set as described above, in particular, the followingadvantageous effects can be obtained in particular.

[0234] (d-1) It is possible to attain a zoom lens which is suited for aphotographic system using a solid-state image sensor, is compact withless constituent lens elements, is corrected particularly for chromaticaberration, and has excellent optical performance, by disposing, inorder from the object side to the image side, a first lens unit ofnegative refractive power, a second lens unit of positive refractivepower and a third lens unit of positive refractive power, effecting thevariation of magnification by varying the separations of the respectiveadjacent lens units, constructing the first lens unit with two lenses,i.e., in order from the object side to the image side, a concave lensand a convex lens, constructing the second lens unit with three lenses,i.e., in order from the object side to the image side, a single convexlens and a cemented lens composed of a concave lens and a convex lens,or a cemented lens composed of a convex lens and a concave lens and asingle convex lens, or a single convex lens and a cemented lens composedof a convex lens and a concave lens, and constructing the third lensunit with at least one convex lens.

[0235] (d-2) It is possible to effectively correct the various off-axialaberrations, such as astigmatism and distortion, and sphericalaberration due to the increase of an aperture ratio, by effectivelyintroducing an aspheric surface into each lens unit.

[0236] Next, numerical data of the numerical examples 6 to 8 of theinvention are shown.

[0237] In addition, the values of the factors in the above-mentionedconditions (5) to (9) for the numerical examples 6 to 8 are listed inTable-2.

NUMERICAL EXAMPLE 6

[0238] f = 5.50-10.60 (mm)  Fno = 2.9-4.0  2ω = 61.4°-34.4° R1 = 20.453D1 = 1.20 N1 = 1.77250 ν1 = 49.6 R2 = 3.694* D2 = 0.90 R3 = 5.082 D3 =2.10 N2 = 1.80518 ν2 = 25.4 R4 = 8.267 D4 = Variable R5 = Stop D5 = 0.50R6 = 13.292* D6 = 1.60 N3 = 1.73077 ν3 = 40.5 R7 = −12.248 D7 = 0.95 R8= −4.673 D8 = 0.60 N4 = 1.76182 ν4 = 26.5 R9 = 23.052 D9 = 2.00 N5 =1.77250 ν5 = 49.6 R10 = −5.042* D10 = Variable R11 = 19.454* D11 = 1.60N6 = 1.60311 ν6 = 60.6 R12 = −1267.560 D12 = Variable R13 = ∞ D13 = 2.80N7 = 1.51633 ν7 = 64.2 R14 = ∞

[0239] Variable Focal Length Separation 5.50 7.79 10.60 6.53 9.17 D47.52 4.27 1.72 5.89 2.88 D10 4.91 9.63 13.06 7.43 11.50 D12 3.41 1.681.23 2.38 1.30

[0240] Aspheric Coefficients: R2 R = 3.69429e+00 K = −9.73942e−01 B =1.43792e−03 C = 2.73074e−05 D = 1.56359e−06 R6 R = 1.32924e+01 K =1.27994e+01 B = −7.85390e−04 C = −6.33445e−05 D = −9.01039e−07 R10 R =−5.04162e+00 K = 8.47026e−01 B = 1.28637e−03 C = 2.36015e−05 D =7.54790e−06 R11 R = 1.94539e+01 K = 0.00000e+00 B = −4.37109e−04 C =1.62332e−05 D = −1.26788e−06

NUMERICAL EXAMPLE 7

[0241] f = 5.20-10.35 (mm)  Fno = 2.8-4.0  2ω = 64.4°-35.2° R1 = 110.720D1 = 1.20 N1 = 1.77250 ν1 = 49.6 R2 = 3.410* D2 = 1.02 R3 = 5.803 D3 =2.00 N2 = 1.80518 ν2 = 25.4 R4 = 18.549 D4 = Variable R5 = Stop D5 =0.50 R6 = 4.856* D6 = 1.90 N3 = 1.77250 ν3 = 49.6 R7 = −9.078 D7 = 0.50N4 = 1.71736 ν4 = 29.5 R8 = 5.069 D8 = 0.42 R9 = 19.306 D9 = 1.60 N5 =1.69680 ν5 = 55.5 R10 = −14.532* D10 = Variable R11 =508.660* D11 = 1.50N6 = 1.69680 ν6 = 55.5 R12 = −13.714 D12 = Variable R13 = ∞ D13 = 2.70N7 = 1.51633 ν7 = 64.2 R14 = ∞

[0242] Variable Focal Length Separation 5.20 7.70 10.35 6.36 9.06 D47.89 4.60 2.13 6.21 3.26 D10 4.85 9.05 11.63 7.15 10.55 D12 2.21 1.201.81 1.50 1.30

[0243] Aspheric Coefficients: R2 R = 3.41414e+00 K = −9.99930e−01 B =1.00175e−03 C = 1.62461e−05 D = −3.70217e−07 R6 R = 4.85608e+00 K =7.96803e−01 B = −1.38408e−03 C = −4.51331e−05 D = −6.60254e−06 R10 R =−1.45325e+01 K = 7.69796e+00 B = 1.06613e−03 C = 7.42392e−05 D =2.58556e−06 R11 R = 5.08660e+02 K = 0.00000e+00 B = −4.51399e−04 C =2.67697e−06 D = −3.21647e−07

NUMERICAL EXAMPLE 8

[0244] f = 6.24-11.97 (mm)  Fno = 2.7-4.0  2ω = 55.4°-30.6° R1 =−408.296 D1 = 1.30 N1 = 1.77250 ν1 = 49.6 R2 = 5.731* D2 = 1.11 R3 =6.705 D3 = 2.00 N2 = 1.84666 ν2 = 23.8 R4 = 9.956 D4 = Variable R5 =Stop D5 = 0.70 R6 = 37.724* D6 = 1.60 N3 = 1.69680 ν3 = 55.5 R7 =−11.263 D7 = 0.15 R8 = 4.068* D8 = 1.90 N4 = 1.69680 ν4 = 55.5 R9 =−10.353 D9 = 0.50 N5 = 1.64769 ν5 = 33.8 R10 = 3.020 D10 = Variable R11= 130.261* D11 = 1.80 N6 = 1.60311 ν6 = 60.6 R12 = −8.133 D12 = VariableR13 = ∞ D13 = 2.70 N7 = 1.51633 ν7 = 64.2 R14 = ∞

[0245] Variable Focal Length Separation 6.24 8.99 11.97 7.54 10.50 D46.61 4.09 2.25 5.29 3.09 D10 4.30 8.27 11.64 6.37 10.03 D12 1.75 1.191.24 1.40 1.14

[0246] Aspheric Coefficients: R2 R = 5.73088e+00 K = −1.98834e+00 B =1.10448e−03 C = 6.36136e−06 D = −1.55169e−07 R6 R = 3.77245e+01 K =−1.10342e+02 B = −1.46479e−04 C = 2.09594e−05 D = −3.06969e−06 R8 R =4.06784e+00 K = −3.30676e−01 B = 4.58158e−04 C = 3.25580e−06 D =2.67999e−06 R11 R = 1.30261e+02 K = 0.00000e+00 B = −9.13704e−04 C =2.07821e−05 D = −7.46835e−07

[0247] TABLE 2 Numerical Example Condition 6 7 8 (5) nd 1.76182 1.717361.64769 (6) νd 26.5 29.5 33.8 (7) X1 0.44 0.74 2.46 X3 2.29 1.03 0.61|X1/X3| 0.20 0.72 4.00 (8) DL1 4.20 4.22 4.41 DL2 5.15 4.42 4.15 DL31.60 1.50 1.80 DL 31.08 29.29 28.60 (DL1 + DL1 + DL3)/DL 0.35 0.35 0.36(9) DA2 0.95 0.42 0.15 DD2 5.15 4.42 4.15 DA2/DD2 0.18 0.09 0.04

[0248] According to the second embodiment, It is possible to attain azoom lens which is suited, in particular, for a photographic systemusing a solid-state image sensor, is compact with less constituent lenselements, and has excellent optical performance.

[0249] (Third Embodiment)

[0250]FIG. 33 to FIGS. 44A to 44D relate to a third embodiment of theinvention, which corresponds to numerical examples 9 to 11 of theinvention to be described later.

[0251]FIG. 33 is a lens block diagram showing a zoom lens according tothe numerical example 9 of the invention. FIGS. 34A to 34D through FIGS.36A to 36D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 9 of the invention.

[0252]FIG. 37 is a lens block diagram showing a zoom lens according tothe numerical example 10 of the invention. FIGS. 38A to 38D throughFIGS. 40A to 40D are graphs showing aberration curves at the wide-angleend, the middle focal length position and the telephoto end,respectively, in the zoom lens according to the numerical example 10 ofthe invention.

[0253]FIG. 41 is a lens block diagram showing a zoom lens according tothe numerical example 11 of the invention. FIGS. 42A to 42D throughFIGS. 43A to 43D are graphs showing aberration curves at the wide-angleend, the middle focal length position and the telephoto end,respectively, in the zoom lens according to the numerical example 11 ofthe invention.

[0254] In the lens block diagrams shown in FIGS. 33, 37 and 41,reference character L1 denotes a first lens unit of negative refractivepower, reference character L2 denotes a second lens unit of positiverefractive power, reference character L3 denotes a third lens unit ofpositive refractive power, reference character SP denotes an aperturestop, reference character IP denotes an image plane, and referencecharacter G denotes a glass block, such as a filter or a colorseparation prism.

[0255] The zoom lens according to the third embodiment has three lensunits, i.e., in order from the object side to the image side, the firstlens unit L1 of negative refractive power, the second lens unit L2 ofpositive refractive power and the third lens unit L3 of positiverefractive power. During zooming from the wide-angle end to thetelephoto end, the first lens unit, the second lens unit and the thirdlens unit each move. More specifically, the first lens unit makes areciprocating motion convex toward the image side, the second lens unitmoves toward the object side, and the third lens unit moves toward theimage side or moves with a locus convex toward the object side.

[0256] In the zoom lens according to the third embodiment, the variationof magnification is effected mainly by moving the second lens unit whilethe shift of an image point due to the variation of magnification iscompensated for by moving forward and backward the first lens unit andmoving the third lens unit toward the image side or moving the thirdlens unit with a locus convex toward the object side.

[0257] The third lens unit shares the increase of a refractive power ofthe photographic lens due to the reduction in size of the image sensor,thereby reducing a refractive power of the short zoom system composed ofthe first and second lens units, so that the occurrence of aberration bylenses constituting the first lens unit can be suppressed, so as toattain high optical performance. Further, the telecentric imageformation on the image side necessary for the photographing apparatus(optical apparatus) using the image sensor or the like is attained bygiving the third lens unit the roll of a field lens.

[0258] Further, the stop SP is disposed on the most object side of thesecond lens unit, thereby shortening the distance between the entrancepupil and the first lens unit on the wide-angle side, so that theincrease of the diameter of lenses constituting the first lens unit canbe prevented. In addition, the various off-axial aberrations arecanceled by the first lens unit and the third lens unit across the stopdisposed on the object side of the second lens unit, so that goodoptical performance can be obtained without increasing the number ofconstituent lenses.

[0259] The zoom lens according to the third embodiment is characterizedin that the third lens unit has at least one positive lens, and thefollowing conditions are satisfied:

ndp3<1.5  (10)

νdp3<70.0  (11)

[0260] where ndp3 and νdp3 are a refractive index and Abbe number,respectively, of material of the positive lens of the third lens unit.

[0261] The conditions (10) and (11) are provided mainly for correctingwell curvature of field and lateral chromatic aberration. If the upperlimit of the condition (10) is exceeded, the Petzval Sum increases inthe negative direction, so that it becomes difficult to correctcurvature of field. Further, if the upper limit of the condition (11) isexceeded, it becomes disadvantageously difficult to correct lateralchromatic aberration at the telephoto end.

[0262] In addition, with the zoom lens according to the third embodimentconstructed as described in the foregoing, the primary object of theinvention can be attained. However, in order to obtain better opticalperformance or in order to attain the reduction in size of the entirelens system, it is preferable to satisfy at least one of the followingconditions (e-1) to (e-16).

[0263] (e-1) During the variation of magnification from the wide-angleend to the telephoto end, the first lens unit moves with a locus convextoward the image side, the second lens unit moves monotonically towardthe object side, and the third lens unit moves toward the image side.

[0264] (e-2) The first lens unit consists of two lenses, i.e., anegative lens and a positive lens, and at least one surface of thenegative lens of the first lens unit is an aspheric surface.

[0265] In the zoom lens according to the third embodiment, the firstlens unit of negative refractive power has the role of causing anoff-axial principal ray to be pupil-imaged on the center of a stop, and,particularly, on the wide-angle side, the amount of refraction of anoff-axial principal ray is large. Therefore, in the first lens unit, thevarious off-axial aberrations, particularly, astigmatism and distortion,are apt to occur.

[0266] Accordingly, similarly to an ordinary wide-angle lens, the firstlens unit is made to have the construction having a negative lens and apositive lens so as to prevent the diameter of a lens disposed on themost object side from increasing. Further, it is more preferable that alens surface on the image side of the negative lens 11 of meniscus formis such an aspheric surface that a negative refractive power becomesprogressively weaker toward a marginal portion of the lens surface. Bythis arrangement, astigmatism and distortion are corrected in awell-balanced manner, and the first lens unit is composed of such asmall number of lenses as two, so that it becomes easy to make theentire lens system compact.

[0267] In addition, in order to prevent the occurrence of an off-axialaberration due to the refraction of an off-axial principal ray, each oflenses constituting the first lens unit has a lens surface approximateto concentric spherical surfaces having the center on a point at whichthe stop and the optical axis intersect.

[0268] (e-3) The following conditions are satisfied:

ndn1>1.70  (12)

νdn1>35.0  (13)

[0269] where ndn1 and νdn1 are a refractive index and Abbe number,respectively, of material of a negative lens included in the first lensunit.

[0270] The conditions (12) and (13) are provided for making thecompactness of the entire lens system and the good imaging performancecompatible with each other.

[0271] If the upper limit of the condition (12) is exceeded, the Petzvalsum of the first lens unit increases in the positive direction, so thatit becomes difficult to correct curvature of field.

[0272] Further, if the upper limit of the condition (13) is exceeded, itbecomes disadvantageously difficult to correct lateral chromaticaberration at the wide-angle end, in particular.

[0273] (e-4) The second lens unit consists of two cemented lenses.

[0274] In the third embodiment, in order to cope with the reduction ofthe amount of chromatic aberration, which is required according to theincreased number of pixels and the minimization of cell pitches of asolid-state image sensor such as a CCD, the second lens unit consists oftwo cemented lenses, i.e., a first cemented lens composed of a positivelens 21 of meniscus form and a negative lens 22 of meniscus formcemented together, and a second cemented lens composed of a negativelens 23 and a positive lens 24 cemented together. By this arrangement,it is possible to correct well longitudinal chromatic aberration andlateral chromatic aberration.

[0275] Further, with the second lens unit consisting of two cementedlenses, the following advantages are obtained. Since a refractive powerof the concave (negative) lens component in the so-called triplet typeis separated into two components, the degree of freedom of thecorrection of aberration is increased as against an aberrationcorrecting method using such a single concave lens component as that inthe triplet type. Accordingly, it becomes unnecessary to correctoff-axial flare, which, otherwise, is corrected by increasing the glassthickness of the concave lens component, or to correct sphericalaberration due to two negative air lenses provided before and behind theconcave lens component. Therefore, it becomes possible to lessen thethickness on the optical axis of the second lens unit as compared withthe triplet type. Thus, the second lens unit composed of two cementedlenses contributes to the shortening of the entire optical system andthe shortening of the total length of the lens system as retracted.

[0276] (e-5) The second lens unit has, on the most object side thereof,a first cemented lens composed of a positive lens having a convexsurface facing the object side and a negative lens having a concavesurface facing the image side, a lens surface on the object side of thepositive lens of the first cemented lens is an aspheric surface, and thefollowing condition is satisfied:

0<(R21−R23)/(R21+R23)<0.1  (14)

[0277] where R21 is a radius of paraxial curvature of the lens surfaceon the object side of the positive lens of the first cemented lens, andR23 is a radius of paraxial curvature of a lens surface on the imageside of the negative lens of the first cemented lens.

[0278] If the upper limit of the condition (14) is exceeded, the Petzvalsum of the second lens unit increases in the negative direction, so thatit becomes difficult to correct curvature of field.

[0279] If the lower limit of the condition (14) is exceeded, it becomesdisadvantageously difficult to correct spherical aberration and coma.

[0280] (e-6) The second lens unit has a positive lens disposed on themost image side thereof, and the following conditions are satisfied:

ndp2>1.70  (15)

νdp2>40.0  (16)

[0281] where ndp2 and νdp2 are a refractive index and Abbe number,respectively, of material of the positive lens of the second lens unit.

[0282] If the upper limit of the condition (15) is exceeded, the Petzvalsum increases in the negative direction, so that it becomes difficult tocorrect curvature of field. Further, if the upper limit of the condition(16) is exceeded, it becomes disadvantageously difficult to correctlongitudinal chromatic aberration at the telephoto end.

[0283] (e-7) The third lens unit consists of one positive lens.

[0284] The third lens unit of positive refractive power consists of onepositive lens 31 having a convex surface facing the object side, andserves also as a field lens for making the zoom lens telecentric on theimage side.

[0285] (e-8) One positive lens of the third lens unit has at least oneaspheric surface.

[0286] In particular, in the third embodiment, it is preferable that alens surface on the image side of the convex lens 31 is such an asphericsurface that a positive refractive power becomes progressively weakertoward a marginal portion of the lens surface. By this arrangement, itis possible to correct the various off-axial aberrations over the entirezooming range.

[0287] (e-9) Focusing from an infinitely distant object to a closestobject is effected by moving the third lens unit toward the object side.

[0288] When focusing from an infinitely distant object to a closestobject is effected by using the zoom lens according to the thirdembodiment, the good optical performance can be obtained by moving thefirst lens unit toward the object side. However, it is more preferableto move the third lens unit toward the object side.

[0289] This arrangement prevents the increase of the diameter of a frontlens member due to the focusing movement of the first lens unit which isdisposed on the most object side, prevents the increase of the load onan actuator for moving the first lens unit which is the heaviest amongthe lens units, and makes it possible to move, during zooming, the firstlens unit and the second lens unit in an interlocking relation simplywith a cam or the like used. Therefore, it is possible to attain thesimplification of a mechanism and the enhancement of precision thereof.

[0290] Further, in a case where focusing is performed by using the thirdlens unit, if the third lens unit is arranged to be moved toward theimage side during the variation of magnification from the wide-angle endto the telephoto end, the telephoto end, at which the amount of movementfor focusing is large, can be located on the image side. Accordingly, itbecomes possible to minimize the amount of total movement of the thirdlens unit required for zooming and focusing. This arrangement makes itpossible to attain the compactness of the entire lens system.

[0291] (e-10) The following condition is satisfied:

0.25<(L1+L2+L3)/L<0.45  (17)

[0292] where L is a distance, at the telephoto end, from a vertex on theobject side of a lens disposed on the most object side of the first lensunit to an image plane, L1 is a distance from the vertex on the objectside of the lens disposed on the most object side of the first lens unitto a vertex on the image side of a lens disposed on the most image sideof the first lens unit, L2 is a distance from a vertex on the objectside of a lens disposed on the most object side of the second lens unitto a vertex on the image side of a lens disposed on the most image sideof the second lens unit, and L3 is a distance from a vertex on theobject side of a lens disposed on the most object side of the third lensunit to a vertex on the image side of a lens disposed on the most imageside of the third lens unit.

[0293] If the upper limit of the condition (17) is exceeded, althoughthe total length of the optical system at the telephoto end becomesshort, the sum of lengths of the respective lens units on the opticalaxis becomes large, so that the total length of the entire lens systemas retracted becomes long disadvantageously.

[0294] If the lower limit of the condition (17) is exceeded, althoughthe sum of lengths of the respective lens units on the optical axisbecomes small, the total length of the optical system at the telephotoend becomes long, and the amount of movement of each lens unit isnecessarily increased. Therefore, the length of a cam ring or the likefor moving each lens unit becomes long, and, as a result, the totallength of the entire lens system as retracted does not become short.

[0295] (e-11) The following condition is satisfied:

0.05<A2/D2<0.2  (18)

[0296] where D2 is the sum of thicknesses on the optical axis of lensesconstituting the second lens unit, and A2 is the sum of air separationsincluded in the second lens unit.

[0297] If the upper limit of the condition (18) is exceeded, the lengthof the second lens unit on the optical axis becomes long, so that itbecomes disadvantageously difficult to attain the compactness of theoptical system.

[0298] If the lower limit of the condition (18) is exceeded, the powerof the air lens becomes small, so that it becomes disadvantageouslydifficult to correct spherical aberration.

[0299] (e-12) The first lens unit of negative refractive power consistsof two lenses, i.e., in order from the object side to the image side, anegative lens 11 of meniscus form having a concave surface facing theimage side, and a positive lens 12 of meniscus form having a convexsurface facing the object side, or consists of three lenses, i.e., inorder from the object side to the image side, a negative lens 11 ofmeniscus form having a convex surface facing the object side, a negativelens 12 of meniscus form having a convex surface facing the object side,and a positive lens 13 of meniscus form having a convex surface facingthe object side, the second lens unit of positive refractive powerconsists of four lenses, i.e., in order from the object side to theimage side, a positive lens 21 of meniscus form having a concave surfacefacing the image side, a negative lens 22 of meniscus form having aconvex surface facing the object side, a negative lens 23 of meniscusform having a convex surface facing the object side, and a positive lens24 of bi-convex form, the positive lens 21 and the negative lens 22constituting a cemented lens, the negative lens 23 and the positive lens24 constituting a cemented lens, and the third lens unit of positiverefractive power consists of a positive lens 31 having a convex surfacefacing the image side or a cemented lens composed of a negative lens anda positive lens.

[0300] By this arrangement, it is possible to easily attain thecompactness of a lens system while keeping good optical performance.

[0301] (e-13) The second lens unit of positive refractive power has, onthe most object side thereof, a positive lens 21 having a strong convexsurface facing the object side. By this arrangement, it is possible tolessen the angle of refraction of an off-axial principal ray havingexited from the first lens unit, thereby preventing the variousoff-axial aberrations from occurring.

[0302] (e-14) A positive lens 21 included in the second lens unit is alens arranged to allow an on-axial ray to pass at the largest height,and is concerned with the correction of, mainly, spherical aberrationand coma. Therefore, it is preferable that a lens surface on the objectside of the positive lens 21 is such an aspheric surface that a positiverefractive power becomes progressively weaker toward a marginal portionof the lens surface. By this arrangement, it becomes easy to correctwell spherical aberration and coma.

[0303] (e-15) A negative lens 22 disposed on the image side of apositive lens 21 on the object side included in the second lens unit ismade to have a concave surface facing the image side, so that a negativeair lens is formed by the concave surface on the image side of thenegative lens 22 and a convex surface on the object side of a negativelens 23 disposed subsequent to the negative lens 22. By thisarrangement, it is possible to correct spherical aberration occurringdue to the increase of an aperture ratio.

[0304] (e-16) When the back focal distance is denoted by sk′, the focallength of the third lens unit is denoted by f3, and the imagemagnification of the third lens unit is denoted by β3, the followingrelation is obtained:

sk′=f3 (1−β3)

[0305] provided that 0<β3<1.0.

[0306] Here, when the third lens unit is moved toward the image sideduring the variation of magnification from the wide-angle end to thetelephoto end, the back focal distance sk′ decreases, so that the imagemagnification β3 of the third lens unit increases on the telephoto side.Then, as a result, the third lens unit shares the variation ofmagnification with the second lens unit, so that the amount of movementof the second lens unit is reduced. Therefore, since such a space forthe movement of the second lens unit can be saved, the third lens unitcontributes to the reduction in size of the lens system.

[0307] Next, characteristic features of the lens construction of each ofthe zoom lenses according to the numerical examples 9 to 11 aredescribed.

NUMERICAL EXAMPLE 9

[0308] The zoom lens according to the numerical example 9 shown in FIG.33 is a zoom lens having the variable magnification ratio of about 3 andthe aperture ratio of 2.7-4.8 or thereabout.

NUMERICAL EXAMPLE 10

[0309] In the zoom lens according to the numerical example 10 shown inFIG. 37, during zooming from the wide-angle end to the telephoto end,the first lens unit makes a reciprocating motion convex toward the imageside, the second lens unit moves toward the object side, and the thirdlens unit moves toward the image side.

[0310] In the numerical example 10, the first lens unit consists ofthree lenses, i.e., in order from the object side to the image side, anegative lens 11 of meniscus form, a negative lens 12 of meniscus formand a positive lens 13 of meniscus form, so that it is possible toeasily attain the further widening of an angle of view as compared witha zoom lens in which the first lens unit is composed of two lenses.

[0311] The zoom lens according to the numerical example 10 is a zoomlens having the variable magnification ratio of about 3 and the apertureratio of 2.6-4.8 or thereabout.

NUMERICAL EXAMPLE 11

[0312] In the zoom lens according to the numerical example 11 shown inFIG. 41, during zooming from the wide-angle end to the telephoto end,the first lens unit makes a reciprocating motion convex toward the imageside, the second lens unit moves toward the object side, and the thirdlens unit moves toward the image side.

[0313] In the numerical example 11, the third lens unit consists of acemented lens composed of a negative lens of meniscus form and apositive lens of bi-convex form, thereby sufficiently correctingchromatic aberration in conjunction with two cemented lenses of thesecond lens unit.

[0314] The zoom lens according to the numerical example 11 is a zoomlens having the variable magnification ratio of about 3.0 and theaperture ratio of 2.7-4.8 or thereabout.

[0315] Next, numerical data of the numerical examples 9 to 11 of theinvention are shown.

[0316] In addition, the values of the factors in the above-mentionedconditions (10) to (18) for the numerical examples 9 to 11 are listed inTable-3.

NUMERICAL EXAMPLE 9

[0317] R1 =206.343 D1 = 1.40 N1 = 1.80238 ν1 = 40.7 R2 = 4.841* D2 =1.87 R3 = 9.750 D3 = 2.00 N2 = 1.84666 ν2 = 23.9 R4 = 49.125 D4 =Variable R5 = Stop D5 = 0.70 R6 = 4.564* D6 = 2.00 N3 = 1.74330 ν3 =49.3 R7 = 10.675 D7 = 0.80 N4 = 1.69895 ν4 = 30.1 R8 = 3.878 D8 = 0.72R9 = 10.459 D9 = 0.50 N5 = 1.84666 ν5 = 23.9 R10 = 6.339 D10 = 1.80 N6 =1.60311 ν6 = 60.6 R11 = −19.132 D11 = Variable R12 = 14.948 D12 = 1.40N7 = 1.48749 ν7 = 70.2 R13 = −48.563 D13 = Variable R14 = ∞ D14 = 2.82N8 = 1.51633 ν8 = 64.1 R15 = ∞

[0318] Variable Focal Length Separation 5.49 10.60 16.18 D4 16.12 5.842.43 D11 3.93 11.43 19.83 D13 4.20 3.82 2.53

[0319] Aspheric Coefficients: R2 R = 4.84094e+00 K = −1.84876e+00 B =1.10500e−03 C = −1.66493e−05 D = 5.13200e−07 E = −2.00144e−08 F =3.39222e−10 R6 R = 4.56367e+00 K = −1.26047e−01 B = −2.89482e−04 C =−9.34418e−06 D = 1.07843e−07 E = −3.76119e−08

NUMERICAL EXAMPLE 10

[0320] R1 = 59.735 D1 = 1.30 N1 = 1.67470 ν1 = 54.9 R2 = 6.518* D2 =2.02 R3 = 21.785 D3 = 0.80 N2 = 1.77250 ν2 = 49.6 R4 = 8.687 D4 = 1.48R5 = 11.006 D5 = 2.00 N3 = 1.84666 ν3 = 23.9 R6 = 33.156 D6 = VariableR7 = Stop D7 = 0.80 R8 = 4.526* D8 = 2.20 N4 = 1.74330 ν4 = 49.3 R9 =11.087 D9 = 0.60 N5 = 1.69895 ν5 = 30.1 R10 = 3.873 D10 = 0.75 R11 =10.369 D11 = 0.50 N6 = 1.84666 ν6 = 23.9 R12 = 6.401 D12 = 1.80 N7 =1.60311 ν7 = 60.6 R13 = −19.975 D13 = Variable R14 = 12.110* D14 = 1.50N8 = 1.48749 ν8 = 70.2 R15 = −54.317 D15 = Variable R16 = ∞ D16 = 2.83N9 = 1.51633 ν9 = 64.1 R17 = ∞

[0321] Variable Focal Length Separation 5.00 9.79 14.98 D6 14.64 5.462.12 D13 4.83 13.24 21.64 D15 3.55 3.02 2.51

[0322] Aspheric Coefficients: R2 R = 6.51783e+00 K = 2.42523e−01 B =−5.97797e−04 C = −1.56333e−06 D = −7.09941e−07 E = 2.27735e−08 F =−6.39051e−10 R8 R = 4.52644e+00 K = −1.27422e−01 B = −3.12555e−04 C =−9.46539e−06 D = 8.23854e−08 E = −3.89693e−08 R14 R = 1.21103e+01 K = 0B = −1.72597e−04 C = 7.00489e−06 D = −1.67824e−07

NUMERICAL EXAMPLE 11

[0323] R1 = 156.481 D1 = 1.30 N1 = 1.80238 ν1 = 40.7 R2 = 5.435* D2 =1.83 R3 = 9.697 D3 = 2.20 N2 = 1.84666 ν2 = 23.9 R4 = 34.098 D4 =Variable R5 = Stop D5 = 0.80 R6 = 4.588* D6 = 2.00 N3 = 1.74330 ν3 =49.3 R7 = 13.399 D7 = 0.60 N4 = 1.69895 ν4 = 30.1 R8 = 3.929 D8 = 0.66R9 = 11.757 D9 = 0.60 N5 = 1.84666 ν5 = 23.9 R10 = 7.899 D10 = 1.70 N6 =1.60311 ν6 = 60.6 R11 = −20.079 D11 = Variable R12 = 25.476 D12 = 0.50N7 = 1.60342 ν7 = 38.0 R13 = 24.901 D13 = 1.60 N8 = 1.49700 ν8 = 81.5R14 = −25.962 D14 = Variable R15 = ∞ D15 = 2.80 N9 = 1.51633 ν9 = 64.1R16 = ∞

[0324] Variable Focal Length Separation 5.64 10.99 16.51 D4 18.32 6.102.69 D11 3.11 9.75 18.27 D14 4.42 4.42 2.54

[0325] Aspheric Coefficients: R2 R = 5.43534e+00 K = −2.28361e+00 B =1.23160e−03 C = −2.40093e−05 D = 8.92996e−07 E = −2.78071e−08 F =3.81774e−10 R6 R = 4.58844e+00 K = −1.27107e−01 B = −2.62331e−04 C =−8.61678e−06 D = 1.99209e−07 E = −3.78975e−08

[0326] TABLE 3 Condition lower upper Numerical Example limit limit 9 1011 (10) ndp3 1.5 1.48749 1.48749 1.49700 (11) νdp3 70 70.2 70.2 81.5(12) ndn1 1.7 1.80238 — 1.80238 (13) νdn1 35 40.7 — 40.7 (14) R21 4.5644.526 4.588 R23 3.878 3.873 3.929 (R21 − R23)/ 0 0.1 0.081 0.078 0.077(R21 + R23) (15) ndp2 1.7 1.74330 1.74330 1.74330 (16) νdp2 40 49.3 49.349.3 (17) L1 5.27 7.60 5.33 L2 5.82 5.85 5.56 L3 1.40 1.50 2.10 L 41.7445.78 41.28 (L1 + L2 + 0.25 0.45 0.30 0.33 0.31 L3)/L (18) A2 0.72 0.750.66 D2 5.82 5.85 5.56 A2/D2 0.05 0.2 0.12 0.13 0.12

[0327] According to the third embodiment of the invention, it ispossible to attain a zoom lens which is suited for a photographic systemusing a solid-state image sensor, has a high variable magnificationratio despite being compact and small in diameter with less constituentlens elements, and has excellent optical performance.

[0328] (Fourth Embodiment)

[0329]FIG. 45 to FIGS. 60A to 60D relate to a fourth embodiment of theinvention, which corresponds to numerical examples 12 to 15 of theinvention to be described later.

[0330]FIG. 45 is a lens block diagram showing a zoom lens according tothe numerical example 12 of the invention. FIGS. 46A to 46D throughFIGS. 48A to 48D are graphs showing aberration curves at the wide-angleend, the middle focal length position and the telephoto end,respectively, in the zoom lens according to the numerical example 12 ofthe invention.

[0331]FIG. 49 is a lens block diagram showing a zoom lens according tothe numerical example 13 of the invention. FIGS. 50A to 50D throughFIGS. 52A to 52D are graphs showing aberration curves at the wide-angleend, the middle focal length position and the telephoto end,respectively, in the zoom lens according to the numerical example 13 ofthe invention.

[0332]FIG. 53 is a lens block diagram showing a zoom lens according tothe numerical example 14 of the invention. FIGS. 54A to 54D throughFIGS. 56A to 56D are graphs showing aberration curves at the wide-angleend, the middle focal length position and the telephoto end,respectively, in the zoom lens according to the numerical example 14 ofthe invention.

[0333]FIG. 57 is a lens block diagram showing a zoom lens according tothe numerical example 15 of the invention. FIGS. 58A to 58D throughFIGS. 60A to 60D are graphs showing aberration curves at the wide-angleend, the middle focal length position and the telephoto end,respectively, in the zoom lens according to the numerical example 15 ofthe invention.

[0334] In the lens block diagrams shown in FIGS. 45, 49, 53 and 57,reference character L1 denotes a first lens unit of negative refractivepower, reference character L2 denotes a second lens unit of positiverefractive power, reference character L3 denotes a third lens unit ofpositive refractive power, reference character SP denotes an aperturestop for determining the brightness of an optical system, referencecharacter IP denotes an image plane, and reference character G denotes aglass block, such as a filter or a color separation prism.

[0335] As shown in the lens block diagrams of FIGS. 45, 49, 53 and 57,the zoom lens according to the fourth embodiment has three lens units,i.e., in order from the object side to the image side, the first lensunit L1 of negative refractive power, the second lens unit L2 ofpositive refractive power and the third lens unit L3 of positiverefractive power. During the variation of magnification from thewide-angle end to the telephoto end, as indicated by the arrows shown inthe lens block diagrams shown in FIGS. 45, 49, 53 and 57, the first lensunit L1 makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side.

[0336] The zoom lens according to the fourth embodiment has the basicconstruction as described above. Then, according to the fourthembodiment, it is possible to attain a zoom lens having high opticalperformance, by making the zoom lens have such a lens construction as tosatisfy at least one of the following conditions (19) to (22):

0.08<M3/fw<0.4  (19)

0.7<|f1/ft|<1.0  (20)

1.45<f3/ft<2.0  (21)

0.63<f2/ft<0.8  (22)

[0337] where M3 is an amount of movement of the third lens unit towardthe image side during the variation of magnification from the wide-angleend to the telephoto end with an infinitely distant object focused on,fw and ft are focal lengths of the zoom lens at the wide-angle end andthe telephoto end, respectively, and f1, f2 and f3 are focal lengths ofthe first lens unit, the second lens unit and the third lens unit,respectively.

[0338] Next, characteristic features of the lens construction of thezoom lens according to the fourth embodiment are described.

[0339] The first lens unit when the zoom lens is at the telephoto end islocated at about the same position as when the zoom lens is at thewide-angle end, or is located slightly nearer to the image side thanwhen the zoom lens is at the wide-angle end. Accordingly, the amount ofmovement of the first lens unit required when the zoom lens is retractedis prevented from becoming too large.

[0340] The aperture stop SP is disposed on the object side of the secondlens unit L2, and is arranged to move along the optical axis integrallywith the second lens unit.

[0341] In the zoom lens according to the fourth embodiment, thevariation of magnification is effected mainly by moving the second lensunit of positive refractive power while the shift of an image point dueto the variation of magnification is compensated for by moving forwardand backward the first lens unit of negative refractive power and movingthe third lens unit of positive refractive power toward the image side.

[0342] The third lens unit of positive refractive power shares theincrease of a refractive power of the photographic lens due to thereduction in size of the image sensor, thereby reducing a refractivepower of the short zoom system composed of the first and second lensunits, so that the occurrence of aberration by lenses constituting thefirst lens unit can be suppressed, so as to attain high opticalperformance. Further, in particular, the telecentric image formation onthe image side necessary for the optical apparatus using the imagesensor or the like is attained by giving the third lens unit the roll ofa field lens.

[0343] Further, the stop SP is disposed on the most object side of thesecond lens unit, thereby shortening the distance between the entrancepupil and the first lens unit on the wide-angle side, so that theincrease of the diameter of lenses constituting the first lens unit canbe prevented. In addition, the various off-axial aberrations arecanceled by the first lens unit and the third lens unit across the stopdisposed on the object side of the second lens unit, so that goodoptical performance can be obtained without increasing the number ofconstituent lenses.

[0344] Further, in the fourth embodiment, the first lens unit ofnegative refractive power is composed of two lenses, i.e., in order fromthe object side to the image side, a negative lens 11 having a concavesurface facing the image side, and a positive lens 12 of meniscus formhaving a convex surface facing the object side, the second lens unit ofpositive refractive power is composed of four lenses, i.e., a positivelens 21 of bi-convex form, a negative lens 22 of bi-concave form, anegative lens 23 of meniscus form having a convex surface facing theobject side, and a positive lens 24 of bi-convex form, the positive lens21 and the negative lens 22 constituting a cemented lens, the negativelens 23 and the positive lens 24 constituting a cemented lens, and thethird lens unit of positive refractive power is composed of a singlepositive lens 31 having a strong convex surface facing the object side.

[0345] With the respective lens units having such a lens construction asto make the desired refractive power arrangement and the correction ofaberration compatible with each other, as described above, it ispossible to attain the compactness of a lens system while keeping thegood optical performance of the lens system. The first lens unit ofnegative refractive power has the role of causing an off-axial principalray to be pupil-imaged on the center of a stop, and, particularly, onthe wide-angle side, the amount of refraction of an off-axial principalray is large. Therefore, in the first lens unit, the various off-axialaberrations, particularly, astigmatism and distortion, are apt to occur.Accordingly, similarly to an ordinary wide-angle lens, the first lensunit is made to have the construction having a negative lens and apositive lens so as to prevent the diameter of a lens disposed on themost object side from increasing. Further, it is preferable that a lenssurface on the image side of the negative lens 11 is such an asphericsurface that a negative refractive power becomes progressively weakertoward a marginal portion of the lens surface. By this arrangement,astigmatism and distortion are corrected in a well-balanced manner, andthe first lens unit is composed of such a small number of lenses as two,so that it becomes easy to make the entire lens system compact.

[0346] The second lens unit of positive refractive power has, on themost object side thereof, the positive lens 21 having a strong convexsurface facing the object side, so that the second lens unit has such ashape as to lessen the angle of refraction of an off-axial principal rayhaving exited from the first lens unit, thereby preventing the variousoff-axial aberrations from occurring. Further, the positive lens 21 is alens arranged to allow an on-axial ray to pass at the largest height,and is concerned with the correction of, mainly, spherical aberrationand coma. In the fourth embodiment, it is preferable that a lens surfaceon the object side of the positive lens 21 is such an aspheric surfacethat a positive refractive power becomes progressively weaker toward amarginal portion of the lens surface. By this arrangement, it becomeseasy to correct well spherical aberration and coma. Further, thenegative lens 22 disposed on the image side of the positive lens 21 ismade to have a concave surface facing the image side, so that a negativeair lens is formed by the lens surface on the image side of the negativelens 22 and a convex surface on the object side of the negative lens 23disposed subsequent to the negative lens 22. Accordingly, it is possibleto correct spherical aberration occurring due to the increase of anaperture ratio.

[0347] In addition, in the fourth embodiment, in order to cope with thereduction of the amount of chromatic aberration, which is requiredaccording to the increased number of pixels and the minimization of cellpitches of a solid-state image sensor such as a CCD, the second lensunit is composed of two cemented lenses. By this arrangement, it ispossible to correct well longitudinal chromatic aberration and lateralchromatic aberration.

[0348] In the zoom lens according to the fourth embodiment, the thirdlens unit is moved toward the image side to make the third lens unithave the function of the variation of magnification and to lessen theburden of the variation of magnification imposed on the second lensunit, so that the amount of movement of the second lens unit is reduced,thereby attaining the reduction in the total lens length.

[0349] Next, the technical significance of each of the above-mentionedconditions (19) to (22) and the lens construction other than thatmentioned in the foregoing are described.

[0350] (f-1) The condition (19) is provided mainly for reducing the sizeof the entire lens system.

[0351] If the amount of movement of the third lens unit becomes toosmall beyond the lower limit of the condition (19), the contribution ofthe third lens unit concerning the variation of magnification becomessmall, necessitating moving the second lens unit much to that extent, sothat the reduction in size of the lens system becomes insufficient. Onthe other hand, if the upper limit of the condition (19) is exceeded, itbecomes difficult to secure the back focal distance at the telephotoend.

[0352] (f-2) The condition (20) is provided mainly for appropriatelysetting the refractive power of the first lens unit so as to correctwell the various aberrations, such as distortion and curvature of field,as well as to secure the sufficient back focal distance, therebyattaining high optical performance.

[0353] If the focal length of the first lens unit becomes short beyondthe lower limit of the condition (20), it becomes difficult to correctthe variation of distortion or curvature of field during the variationof magnification. On the other hand, if the upper limit of the condition(20) is exceeded, it becomes difficult to secure the back focaldistance.

[0354] (f-3) When a close-distance object is to be photographed by usingthe zoom lens according to the fourth embodiment, the good opticalperformance can be obtained by moving the first lens unit toward theobject side. However, it is preferable to move the third lens unit alsotoward the object side. This arrangement prevents the increase of thediameter of a front lens member due to the focusing movement of thefirst lens unit which is disposed on the most object side, prevents theincrease of the load on an actuator for moving the first lens unit whichis the heaviest among the lens units, and makes it possible to move,during zooming, the first lens unit and the second lens unit in aninterlocking relation simply with a cam or the like used. Therefore, itis possible to attain the simplification of a mechanism and theenhancement of precision thereof.

[0355] (f-4) The condition (21) is provided for making the zoom lenshave a more telecentric construction than the two-unit constructionmerely composed of a negative lens unit and a positive lens unit, byadditionally providing the third lens unit of positive refractive power,and is provided for making the effect of the telecentric constructionsufficient.

[0356] If the focal length of the third lens unit becomes too shortbeyond the lower limit of the condition (21), the composite focal lengthof the first lens unit and the second lens unit becomes long to thatextent, so that the compactness of the entire lens system becomesinsufficient. On the other hand, if the upper limit of the condition(21) is exceeded, the exit pupil becomes too short, in particular, atthe wide-angle end, and, in a case where focusing is effected by usingthe third lens unit, the amount of movement required for focusingincreases disadvantageously.

[0357] (f-5) The condition (22) is provided for reducing the amount ofmovement of the second lens unit required for the variation ofmagnification, to attain the reduction in size of the entire lenssystem.

[0358] If the focal length of the second lens unit becomes short beyondthe lower limit of the condition (22), although an advantage arises inreducing the size of the lens system, the Petzval sum becomes too largein the positive direction, so that it becomes difficult to correctcurvature of field. On the other hand, if the upper limit of thecondition (22) is exceeded, the amount of movement of the second lensunit required for the variation of magnification becomes large, so thatit becomes difficult to attain the reduction in size of the lens system.

[0359] (f-6) In the fourth embodiment, with the second lens unitconsisting of two cemented lenses, the following advantages areobtained. Since a refractive power of the concave (negative) lenscomponent in the so-called triplet type is separated into twocomponents, the degree of freedom of the correction of aberration isincreased as against an aberration correcting method using such a singleconcave lens component as that in the triplet type. Accordingly, itbecomes unnecessary to correct off-axial flare, which, otherwise, iscorrected by increasing the glass thickness of the concave lenscomponent, or to correct spherical aberration due to two negative airlenses provided before and behind the concave lens component. Therefore,it becomes possible to lessen the thickness on the optical axis of thesecond lens unit as compared with the triplet type. Thus, the secondlens unit composed of two cemented lenses contributes to the shorteningof the entire optical system and the shortening of the total length ofthe lens system as retracted.

[0360] (f-7) It is desirable that the third lens unit is composed of asingle positive lens, from the viewpoints of the size of the lens systemand the reduction of load imposed on an actuator required for focusing.In this instance, it is preferable to satisfy the following condition:

−1.5<(R3f+R3r)/(R3f−R3r)<−0.5  (23)

[0361] where R3f is a radius of curvature of a lens surface on theobject side of the single positive lens, and R3r is a radius ofcurvature of a lens surface on the image side of the single positivelens.

[0362] The condition (23) is provided for, when the third lens unit is asingle positive lens of spherical form, appropriately setting the shapeof the single positive lens so as to enable focusing to be effectedwhile lessening the variation of aberration.

[0363] If the lower limit of the condition (23) is exceeded, the ghostoccurring due to the interreflection between the image pickup surfaceand the lens surface on the object side of the single positive lens ofthe third lens unit becomes apt to be formed in the vicinity of theimage pickup surface. If it is intended to avoid this ghost, it becomesnecessary to take the excessive back focal distance, thereby making itdifficult to sufficiently reduce the size of the lens system. On theother hand, if the upper limit of the condition (23) is exceeded, in acase where focusing is effected by using the third lens unit, it becomesdifficult to correct spherical aberration and astigmatism caused by thefocusing.

[0364] (f-8) If such an aspheric surface that a positive refractivepower becomes progressively weaker toward a marginal portion thereof isintroduced into the third lens unit, it is possible to further reducethe variation of astigmatism during the variation of magnification.

[0365] According to the fourth embodiment of the invention, it ispossible to attain a zoom lens which is suited for a photographic systemusing a solid-state image sensor, is compact with less constituent lenselements, is corrected particularly for chromatic aberration, and hasexcellent optical performance, by constructing the zoom lens with threelens units, i.e., in order from the object side to the image side, afirst lens unit of negative refractive power, a second lens unit ofpositive refractive power and a third lens unit of positive refractivepower, effecting the variation of magnification by varying theseparation between the respective adjacent lens units, and appropriatelysetting the refractive power arrangement, the amount of movement and theshape of each lens unit.

[0366] Further, it is possible to effectively correct the variousoff-axial aberrations, particularly, astigmatism and distortion, andspherical aberration caused by the increase of an aperture ratio, byintroducing an aspheric surface into each lens unit.

[0367] Next, numerical data of the numerical examples 12 to 15 of theinvention are shown.

[0368] In addition, the values of the factors in the above-mentionedconditions (19) to (23) for the numerical examples 12 to 15 are listedin Table-4.

NUMERICAL EXAMPLE 12

[0369] f = 1-2.83  Fno = 2.87-4.90  2ω = 59.5°-22.8° R1 = 10.855 D1 =0.21 N1 = 1.802380 ν1 = 40.8 R2 = 0.830* D2 = 0.31 R3 = 1.545 D3 = 0.29N2 = 1.846660 ν2 = 23.9 R4 = 4.768 D4 = Variable R5 = Stop D5 = 0.11 R6= 0.885* D6 = 0.43 N3 = 1.802380 ν3 = 40.8 R7 = −5.079 D7 = 0.10 N4 =1.698947 ν4 = 30.1 R8 = 0.720 D8 = 0.08 R9 = 2.210 D9 = 0.09 N5 =1.698947 ν5 = 30.1 R10 = 0.944 D10 = 0.31 N6 = 1.603112 ν6 = 60.6 R11 =−3.065 D11 = Variable R12 = 2.292 D12 = 0.21 N7 = 1.518229 ν7 = 58.9 R13=144.538 D13 = 0.43 R14 = ∞ D14 = 0.44 N8 = 1.516330 ν8 = 64.1 R15 = ∞

[0370] Variable Focal Length Separation 1.00 2.41 2.83 D4 2.57 0.54 0.32D11 0.87 2.62 3.11

[0371] Aspheric Coefficients: R2 K = −1.30000e+00 B = 1.19770e−01 C =6.17069e−02 D = −1.61837e−01 E = 1.55951e−01 F = −4.47577e−02 R6 K =−6.96530e−02 B = −6.61431e−02 C = −4.49055e−02 D = −6.81707e−02 E =−4.05399e−02 F = 0.00000e+00

NUMERICAL EXAMPLE 13

[0372] f = 1-2.83  Fno = 2.86-4.90  2ω = 59.5°-22.8° R1 = 9.686 D1 =0.21 N1 = 1.802380 ν1 = 40.8 R2 = 0.838* D2 = 0.31 R3 = 1.532 D3 = 0.29N2 = 1.846660 ν2 = 23.9 R4 = 4.456 D4 = Variable R5 = Stop D5 = 0.11 R6= 0.884* D6 = 0.44 N3 = 1.743300 ν3 = 49.3 R7 = −3.817 D7 = 0.10 N4 =1.603420 ν4 = 38.0 R8 = 0.715 D8 = 0.09 R9 = 2.243 D9 = 0.09 N5 =1.698947 ν5 = 30.1 R10 = 0.828 D10 = 0.31 N6 = 1.603112 ν6 = 60.6 R11 =−3.729 D11 = Variable R12 = 2.648 D12 = 0.21 N7 = 1.603112 ν7 = 60.6 R13= 44.247 D13 = 0.43 R14 = ∞ D14 = 0.44 N8 = 1.516330 ν8 = 64.1 R15 = ∞

[0373] Variable Focal Length Separation 1.00 2.40 2.83 D4 2.60 0.54 0.32D11 0.77 2.54 3.05

[0374] Aspheric Coefficients: R2 K = −1.30000e+00 B = 1.18880e−01 C =8.30828e−02 D = −2.46182e−01 E = 3.32011e−01 F = −1.68932e−01 R6 K =−9.46702e−02 B = −7.14402e−02 C = −3.93806e−02 D = −9.10926e−02 E =−4.05399e−02 F = 0.00000e+00

NUMERICAL EXAMPLE 14

[0375] f = 1-2.83  Fno = 2.86-4.90  2ω = 58.0°-22.2° R1 = 40.701 D1 =0.21 N1 = 1.806100 ν1 = 40.7 R2 = 0.876* D2 = 0.28 R3 = 1.641 D3 = 0.31N2 = 1.846660 ν2 = 23.9 R4 = 7.676 D4 = Variable R5 = Stop D5 = 0.11 R6= 0.797* D6 = 0.37 N3 = 1.743300 ν3 = 49.3 R7 = 38.519 D7 = 0.08 N4 =1.647689 ν4 = 33.8 R8 = 0.674 D8 = 0.09 R9 = 2.419 D9 = 0.07 N5 =1.846660 ν5 = 23.9 R10 = 1.359 D10 = 0.25 N6 = 1.603112 ν6 = 60.6 R11 =−2.632 D11 = Variable R12 = 3.108* D12 = 0.24 N7 = 1.589130 ν7 = 61.3R13 = −25.016 D13 = 0.42 R14 = ∞ D14 = 0.43 N8 = 1.516330 ν8 = 64.1 R15= ∞

[0376] Variable Focal Length Separation 1.00 2.39 2.83 D4 2.58 0.51 0.27D11 0.72 2.55 3.04

[0377] Aspheric Coefficients: R2 K = −2.25821e+00 B = 2.69487e−01 C =−1.72442e−01 D = 1.53228e−01 E = −1.20333e−01 F = 4.19943e−02 R6 K =−9.88795e−02 B = −7.77363e−02 C = −4.83226e−02 D = −1.69170e−01 E =7.89854e−03 F = 0.00000e+00 R12 K = −2.86549e+00 B = −2.19540e−02 C =1.90603e−01 D = −6.03124e−01 E = 7.17200e−01 F = −5.29660e−02

[0378] NUMERICAL EXAMPLE 15 f = 1-2.95  Fno = 2.77-4.80  2ω =61.7°-22.9° R1 = 11.859 D1 = 0.23 N1 = 1.802380 ν1 = 40.7 R2 = 0.886* D2= 0.35 R3 = 1.689 D3 = 0.38 N2 = 1.846660 ν2 = 23.9 R4 = 5.373 D4 =Variable R5 = Stop D5 = 0.12 R6 = 0.868* D6 = 0.40 N3 = 1.743300 ν3 =49.3 R7 = 2.419 D7 = 0.11 N4 = 1.647689 ν4 = 33.8 R8 = 0.732 D8 = 0.12R9 = 1.890 D9 = 0.09 N5 = 1.846660 ν5 = 23.9 R10 = 1.093 D10 = 0.33 N6 =1.603112 ν6 = 60.6 R11 = −3.344 D11 = Variable R12 = 2.445 D12 = 0.27 N7= 1.487490 ν7 = 70.2 R13 = −37.684 D13 = 0.45 R14 = ∞ D14 = 0.46 N8 =1.516330 ν8 = 64.1 R15 = ∞

[0379] Variable Focal Length Separation 1.00 2.50 2.95 D4 2.98 0.60 0.35D11 0.83 2.82 3.36

[0380] Aspheric Coefficients: R2 K = −1.55665e+00 B = 1.47610e−01 C =−2.95829e−02 D = 3.79213e−02 E = −5.88716e−02 F = 3.154797e−02 R6 K =−1.02390e−01 B = −5.07761e−02 C = −3.18134e−02 D = −5.79304e−02 E =−2.08294e−02 F = 0.00000e+00

[0381] TABLE 4 Numerical Example Condition 12 13 14 15 (19) M3/fw 0.1730.241 0.324 0.173 (20) |f1/ft| 0.838 0.855 0.890 0.857 (21) f3/ft 1.5881.648 1.665 1.600 (22) f2/ft 0.719 0.720 0.725 0.759 (23) (R3f + R3r)/−1.032 −1.127 — −0.878 (R3f − R3r)

[0382] According to the fourth embodiment of the invention, it ispossible to attain a zoom lens which is compact and small in diameterwith less constituent lens elements, has a high variable magnificationratio and has excellent optical performance.

[0383] Next, a video camera (optical apparatus) using, as a photographicoptical system, a zoom lens set forth in any one of the above numericalexamples 1 to 15 is described as an embodiment of the invention withreference to FIG. 61.

[0384] Referring to FIG. 61, the video camera includes a video camerabody 110, a photographic optical system 111 composed of a zoom lensaccording to the invention, an image sensor 112, such as a CCD, arrangedto receive an object image formed through the photographic opticalsystem 111, a recording means 113 for recording the object imagereceived by the image sensor 112, and a viewfinder 114 used forobserving an object image displayed on a display element (not shown).The display element is composed of a liquid crystal panel or the like,and is arranged to display thereon the object image formed on the imagesensor 112.

[0385] As described above, by applying a zoom lens according to theinvention to an optical apparatus, such as a video camera, it ispossible to realize an optical apparatus which is small in size and hashigh optical performance.

1. A zoom lens, comprising, in order from an object side to an imageside: a first lens unit of negative optical power, said first lens unitincluding a negative meniscus lens having a concave surface facing theimage side and a positive meniscus lens having a convex surface facingthe object side; a second lens unit of positive optical power, saidsecond lens unit including a cemented lens of positive optical power asa whole disposed on the most image side of said second lens unit, and alens having a concave surface facing the image side and adjoining asurface on the object side of the cemented lens; and a third lens unitof positive optical power, wherein a separation between said first lensunit and said second lens unit and a separation between said second lensunit and said third lens unit are varied to effect variation ofmagnification.
 2. A zoom lens according to claim 1, wherein said zoomlens satisfies the following conditions: 0.5<fc/f2<2.00.5<(Ra+Rb)/(Ra−Rb)<2.5 where fc is a focal length of the cemented lensin said second lens unit, f2 is a focal length of said second lens unit,Ra is a radius of curvature of the surface on the object side of thecemented lens in said second lens unit, and Rb is a radius of curvatureof the surface on the image side of the lens having the concave surfacefacing the image side in said second lens unit.
 3. A zoom lens accordingto claim 1, wherein said second lens unit comprises, in order from theobject side to the image side, a positive lens having a convex surfacefacing the object side, a negative lens having a concave surface facingthe image side, and a cemented lens of positive optical power.
 4. A zoomlens according to claim 1, wherein said third lens unit consists of onepositive lens or a cemented lens of positive optical power as a whole.5. A zoom lens according to claim 1, wherein at least one of negativelenses included in said first lens unit is an aspheric lens, an asphericsurface of said aspheric lens having such a shape that a divergingaction becomes progressively weaker from an optical axis toward amarginal portion of the aspheric surface.
 6. A zoom lens according toclaim 1, wherein at least one of positive lenses included in said secondlens unit is an aspheric lens, an aspheric surface of said aspheric lenshaving such a shape that a converging action becomes progressivelyweaker from an optical axis toward a marginal portion of the asphericsurface.
 7. A zoom lens according to claim 1, wherein said third lensunit includes an aspheric lens of positive optical power, an asphericsurface of said aspheric lens having such a shape that a convergingaction becomes progressively weaker from an optical axis toward amarginal portion of the aspheric surface.
 8. A zoom lens according toclaim 1, wherein said third lens unit moves during the variation ofmagnification.
 9. A zoom lens, comprising, in order from an object sideto an image side: a first lens unit of negative optical power, saidfirst lens unit including a negative meniscus lens having a concavesurface facing the image side and a positive meniscus lens having aconvex surface facing the object side; a second lens unit of positiveoptical power, said second lens unit including a negative lens ofbi-concave form, a positive lens disposed on the object side of thenegative lens of bi-concave form and having a convex surface facing theobject side, and a cemented lens of positive optical power as a wholedisposed on the image side of the negative lens of bi-concave form; anda third lens unit of positive optical power, wherein a separationbetween said first lens unit and said second lens unit and a separationbetween said second lens unit and said third lens unit are varied toeffect variation of magnification.
 10. A zoom lens according to claim 9,wherein said second lens unit includes a positive lens disposed on themost object side thereof and having a convex surface facing the objectside.
 11. A zoom lens according to claim 10, wherein said zoom lenssatisfies the following conditions: 0.3<|fn|/f2<2.00<(Rd+Rc)/(Rd−Rc)<2.5 where fn is a focal length of the negative lens ofbi-concave form in said second lens unit, f2 is a the focal length ofsaid second lens unit, Rc and Rd are radii of curvature of lens surfaceson the object side and the image side, respectively, of the positivelens disposed on the most object side of said second lens unit andhaving the convex surface facing the object side.
 12. A zoom lensaccording to claim 9, wherein said third lens unit consists of onepositive lens or a cemented lens of positive optical power as a whole.13. A zoom lens according to claim 9, wherein at least one of negativelenses included in said first lens unit is an aspheric lens, an asphericsurface of said aspheric lens having such a shape that a divergingaction becomes progressively weaker from an optical axis toward amarginal portion of the aspheric surface.
 14. A zoom lens according toclaim 9, wherein at least one of positive lenses included in said secondlens unit is an aspheric lens, an aspheric surface of said aspheric lenshaving such a shape that a converging action becomes progressivelyweaker from an optical axis toward a marginal portion of the asphericsurface.
 15. A zoom lens according to claim 9, wherein said third lensunit includes an aspheric lens of positive optical power, an asphericsurface of said aspheric lens having such a shape that a convergingaction becomes progressively weaker from an optical axis toward amarginal portion of the aspheric surface.
 16. A zoom lens according toclaim 9, wherein said third lens unit moves during the variation ofmagnification.
 17. A zoom lens, comprising, in order from an object sideto an image side: a first lens unit of negative optical power, saidfirst lens unit including a negative meniscus lens having a concavesurface facing the image side and a positive meniscus lens having aconvex surface facing the object side; a second lens unit of positiveoptical power, said second lens unit including, in order from the objectside to the image side, one or two positive lenses, a negative lens ofbi-concave form, and a cemented lens of positive optical power as awhole; and a third lens unit of positive optical power, wherein aseparation between said first lens unit and said second lens unit and aseparation between said second lens unit and said third lens unit arevaried to effect variation of magnification, and wherein said zoom lenssatisfies the following conditions: 0.5<fc/f2<2.00.5<(Ra+Rb)/(Ra−Rb)<2.5 0.3<|fn|/f2<2.0 0.5<(Rd+Rc)/(Rd−Rc)<2.5 where fcis a focal length of the cemented lens in said second lens unit, fn is afocal length of the negative lens in said second lens unit, f2 is afocal length of said second lens unit, Ra is a radius of curvature of asurface on the object side of the cemented lens in said second lensunit, Rb is a radius of curvature of a surface on the image side of thenegative lens in said second lens unit, and Rc and Rd are radii ofcurvature of lens surfaces on the object side and the image side,respectively, of the positive lens disposed on the most object side ofsaid second lens unit.
 18. A zoom lens, comprising, in order from anobject side to an image side: a first lens unit of negative opticalpower, said first lens unit including a negative lens and a positivelens; a second lens unit of positive optical power, said second lensunit consisting of a cemented lens and one positive lens; and a thirdlens unit of positive optical power, said third lens unit including apositive lens, wherein a separation between said first lens unit andsaid second lens unit and a separation between said second lens unit andsaid third lens unit are varied to effect variation of magnification.19. A zoom lens according to claim 18, wherein said first lens unitconsists of a negative lens and a positive lens.
 20. A zoom lensaccording to claim 18, wherein said second lens unit consists of, inorder from the object side to the image side, a cemented lens and apositive lens.
 21. A zoom lens according to claim 18, wherein saidsecond lens unit consists of, in order from the object side to the imageside, a positive lens and a cemented lens.
 22. A zoom lens according toclaim 18, wherein said third lens unit consists of one positive lens.23. A zoom lens according to claim 18, wherein said zoom lens satisfiesthe following conditions: nd<1.8 νd<40 where nd and νd are a refractiveindex and Abbe number, respectively, of material of a negative lensincluded in said second lens unit.
 24. A zoom lens according to claim18, wherein said zoom lens satisfies the following condition:0.1<X1/X3|<7.0 where X1 is a distance on an optical axis between aposition at which said first lens unit is located on the most objectside and a position at which said first lens unit is located on the mostimage side during the variation of magnification from a wide-angle endto a telephoto end, and X3 is a distance on the optical axis between aposition at which said third lens unit is located on the most objectside and a position at which said third lens unit is located on the mostimage side during the variation of magnification from the wide-angle endto the telephoto end when an object distance is infinity.
 25. A zoomlens according to claim 18, wherein said zoom lens satisfies thefollowing condition: 0.25<(DL1+DL2+DL3)/DL<0.45 where DL is a distance,at a telephoto end, from a vertex on the object side of a lens disposedon the most object side of said first lens unit to an image plane, DL1is a distance from the vertex on the object side of the lens disposed onthe most object side of said first lens unit to a vertex on the imageside of a lens disposed on the most image side of said first lens unit,DL2 is a distance from a vertex on the object side of a lens disposed onthe most object side of said second lens unit to a vertex on the imageside of a lens disposed on the most image side of said second lens unit,and DL3 is a distance from a vertex on the object side of a lensdisposed on the most object side of said third lens unit to a vertex onthe image side of a lens disposed on the most image side of said thirdlens unit.
 26. A zoom lens according to claim 18, wherein said zoom lenssatisfies the following condition: 0.02<DA2/DD2<0.25 where DD2 is thesum of thicknesses on an optical axis of lenses constituting said secondlens unit, and DA2 is the sum of air separations included in said secondlens unit.
 27. A zoom lens according to claim 18, wherein said thirdlens unit moves toward the object side during focusing from aninfinitely distant object to a closest object.
 28. A zoom lens,comprising, in order from an object side to an image side: a first lensunit of negative optical power; a second lens unit of positive opticalpower; and a third lens unit of positive optical power, said third lensunit consisting of one or two lenses including a positive lens, whereina separation between said first lens unit and said second lens unit anda separation between said second lens unit and said third lens unit arevaried to effect variation of magnification, and wherein said zoom lenssatisfies the following conditions: ndp3<1.5 νdp3>70.0 where ndp3 andνdp3 are a refractive index and Abbe number, respectively, of materialof the positive lens in said third lens unit.
 29. A zoom lens accordingto claim 28, wherein, during the variation of magnification from awide-angle end to a telephoto end, said first lens unit moves with alocus convex toward the image side, said second lens unit movesmonotonically toward the object side, and said third lens unit movestoward the image side.
 30. A zoom lens according to claim 28, whereinsaid first lens unit consists of a negative lens and a positive lens,the negative lens of said first lens unit being an aspheric lens.
 31. Azoom lens according to claim 28, wherein said zoom lens satisfies thefollowing conditions: ndn1>1.70 νdn1>35.0 where ndn1 and νdn1 are arefractive index and Abbe number, respectively, of material of anegative lens included in said first lens unit.
 32. A zoom lensaccording to claim 28, wherein said second lens unit consists of twocemented lenses.
 33. A zoom lens according to claim 28, wherein saidsecond lens unit has, on the most object side thereof, a cemented lenscomposed of a positive lens having a convex surface facing the objectside and a negative lens having a concave surface facing the image side,a lens surface on the object side of the positive lens of the cementedlens being an aspheric surface, and said zoom lens satisfies thefollowing condition: 0<(R21−R23)/(R21+R23)<0.1 where R21 is a radius ofparaxial curvature of the lens surface on the object side of thepositive lens of the cemented lens, and R23 is a radius of paraxialcurvature of a lens surface on the image side of the negative lens ofthe cemented lens.
 34. A zoom lens according to claim 28, wherein saidsecond lens unit has a positive lens disposed on the most image sidethereof, and said zoom lens satisfies the following conditions:ndp2>1.70 νdp2>40.0 where ndp2 and νdp2 are a refractive index and Abbenumber, respectively, of material of the positive lens of the secondlens unit.
 35. A zoom lens according to claim 28, wherein said thirdlens unit consists of one positive lens.
 36. A zoom lens according toclaim 35, wherein the positive lens of said third lens unit is anaspheric surface.
 37. A zoom lens according to claim 28, wherein, duringthe variation of magnification from a wide-angle end to a telephoto end,said third lens unit moves toward the object side.
 38. A zoom lensaccording to claim 28, wherein said zoom lens satisfies the followingcondition: 0.25<(L1+L2+L3)/L<0.45 where L is a distance, at a telephotoend, from a vertex on the object side of a lens disposed on the mostobject side of said first lens unit to an image plane, L1 is a distancefrom the vertex on the object side of the lens disposed on the mostobject side of said first lens unit to a vertex on the image side of alens disposed on the most image side of said first lens unit, L2 is adistance from a vertex on the object side of a lens disposed on the mostobject side of said second lens unit to a vertex on the image side of alens disposed on the most image side of said second lens unit, and L3 isa distance from a vertex on the object side of a lens disposed on themost object side of said third lens unit to a vertex on the image sideof a lens disposed on the most image side of said third lens unit.
 39. Azoom lens according to claim 28, wherein said zoom lens satisfies thefollowing condition: 0.05<A2/D2<0.2 where D2 is the sum of thicknesseson an optical axis of lenses constituting said second lens unit, and A2is the sum of air separations included in said second lens unit.
 40. Azoom lens, comprising, in order from an object side to an image side: afirst lens unit of negative optical power; a second lens unit ofpositive optical power; and a third lens unit of positive optical power,wherein a separation between said first lens unit and said second lensunit and a separation between said second lens unit and said third lensunit are varied to effect variation of magnification, and wherein,during the variation of magnification from a wide-angle end to atelephoto end with an infinitely distant object focused on, said thirdlens unit moves monotonically toward the image side or moves with alocus convex toward the image side, and said zoom lens satisfies thefollowing condition: 0.08<M3/fw<0.4 where M3 is an amount of movement ofsaid third lens unit toward the image side during the variation ofmagnification from the wide-angle end to the telephoto end with aninfinitely distant object focused on, and fw is a focal length of saidzoom lens at the wide-angle end.
 41. A zoom lens according to claim 40,wherein said zoom lens satisfies the following condition: 1.45<f3/ft<2.0where f3 is a focal length of said third lens unit, and ft is a focallength of said zoom lens at the telephoto end.
 42. A zoom lens accordingto claim 40, wherein said zoom lens satisfies the following condition:0.63<f2/ft<0.8 where f2 is a focal length of said second lens unit, andft is a focal length of said zoom lens at the telephoto end.
 43. A zoomlens according to claim 40, wherein said third lens unit consists of onepositive lens.
 44. A zoom lens according to claim 43, wherein said zoomlens satisfies the following condition: 1.5<(R3f+R3r)/(R3f−R3r)<−0.5where R3f is a radius of curvature of a lens surface on the object sideof the positive lens of said third lens unit, and R3r is a radius ofcurvature of a lens surface on the image side of the positive lens ofsaid third lens unit.
 45. A zoom lens according to claim 40, whereinsaid second lens unit consists of two cemented lenses.
 46. A zoom lensaccording to claim 40, wherein said third lens unit moves toward theobject side during focusing from an infinitely distant object to aclosest object.
 47. A zoom lens, comprising, in order from an objectside to an image side: a first lens unit of negative optical power, saidfirst lens unit consisting of, in order from the object side to theimage side, a negative lens and a positive lens; a second lens unit ofpositive optical power; and a third lens unit of positive optical power,wherein a separation between said first lens unit and said second lensunit and a separation between said second lens unit and said third lensunit are varied to effect variation of magnification, wherein, with aninfinitely distant object focused on, said third lens unit is locatednearer to the image side at a telephoto end than at a wide-angle end,and wherein said zoom lens satisfies the following condition:0.7<|f1/ft|<1.0 where f1 is a focal length of said first lens unit, andft is a focal length of said zoom lens at the telephoto end.
 48. A zoomlens according to claim 47, wherein said zoom lens satisfies thefollowing condition: 1.45<f3/ft<2.0 where f3 is a focal length of saidthird lens unit, and ft is a focal length of said zoom lens at thetelephoto end.
 49. A zoom lens according to claim 47, wherein said zoomlens satisfies the following condition: 0.63<f2/ft<0.8 where f2 is afocal length of said second lens unit, and ft is a focal length of saidzoom lens at the telephoto end.
 50. A zoom lens according to claim 47,wherein said third lens unit consists of one positive lens.
 51. A zoomlens according to claim 50, wherein said zoom lens satisfies thefollowing condition: 1.5<(R3f+R3r)/(R3f−R3r)<−0.5 where R3f is a radiusof curvature of a lens surface on the object side of the positive lensof said third lens unit, and R3r is a radius of curvature of a lenssurface on the image side of the positive lens of said third lens unit.52. A zoom lens according to claim 47, wherein said second lens unitconsists of two cemented lenses.
 53. A zoom lens according to claim 47,wherein said third lens unit moves toward the object side duringfocusing from an infinitely distant object to a closest object.
 54. Azoom lens, comprising, in order from an object side to an image side: afirst lens unit of negative optical power, said first lens unitconsisting of, in order from the object side to the image side, anegative lens and a positive lens; a second lens unit of positiveoptical power; and a third lens unit of positive optical power, focusingbeing effected by moving said third lens unit, wherein a separationbetween said first lens unit and said second lens unit and a separationbetween said second lens unit and said third lens unit are varied toeffect variation of magnification, and wherein, during the variation ofmagnification from a wide-angle end to a telephoto end with aninfinitely distant object focused on, said third lens unit movesmonotonically toward the image side or moves with a locus convex towardthe image side, and said zoom lens satisfies the following conditions:0.08<M3/fw<0.4 0.7<|f1/ft|<1.0 1.45<f3/ft<2.0 0.63<f2/ft<0.8 where M3 isan amount of movement of said third lens unit toward the image sideduring the variation of magnification from the wide-angle end to thetelephoto end with an infinitely distant object focused on, fw and ftare focal lengths of said zoom lens at the wide-angle end and thetelephoto end, respectively, and f1, f2 and f3 are focal lengths of saidfirst lens unit, said second lens unit and said third lens unit,respectively.
 55. A zoom lens according to claim 54, wherein said thirdlens unit consists of one positive lens, and said zoom lens satisfiesthe following condition: 1.5<(R3f+R3r)/(R3f−R3r)<−0.5 where R3f is aradius of curvature of a lens surface on the object side of the positivelens of said third lens unit, and R3r is a radius of curvature of a lenssurface on the image side of the positive lens of said third lens unit.56. An optical apparatus, comprising: a zoom lens according to claim 1.57. An optical apparatus, comprising: a zoom lens according to claim 9.58. An optical apparatus, comprising: a zoom lens according to claim 17.59. An optical apparatus, comprising: a zoom lens according to claim 18.60. An optical apparatus, comprising: a zoom lens according to claim 28.61. An optical apparatus, comprising: a zoom lens according to claim 40.62. An optical apparatus, comprising: a zoom lens according to claim 47.63. An optical apparatus, comprising: a zoom lens according to claim 54.